AVCONV(1)AVCONV(1)NAMEavconv - avconv video converter
SYNOPSISavconv [global options] [[infile options][-i infile]]... {[outfile
options] outfile}...
DESCRIPTIONavconv is a very fast video and audio converter that can also grab from
a live audio/video source. It can also convert between arbitrary sample
rates and resize video on the fly with a high quality polyphase filter.
avconv reads from an arbitrary number of input "files" (which can be
regular files, pipes, network streams, grabbing devices, etc.),
specified by the "-i" option, and writes to an arbitrary number of
output "files", which are specified by a plain output filename.
Anything found on the command line which cannot be interpreted as an
option is considered to be an output filename.
Each input or output file can in principle contain any number of
streams of different types (video/audio/subtitle/attachment/data).
Allowed number and/or types of streams can be limited by the container
format. Selecting, which streams from which inputs go into output, is
done either automatically or with the "-map" option (see the Stream
selection chapter).
To refer to input files in options, you must use their indices
(0-based). E.g. the first input file is 0, the second is 1 etc.
Similarly, streams within a file are referred to by their indices. E.g.
"2:3" refers to the fourth stream in the third input file. See also the
Stream specifiers chapter.
As a general rule, options are applied to the next specified file.
Therefore, order is important, and you can have the same option on the
command line multiple times. Each occurrence is then applied to the
next input or output file. Exceptions from this rule are the global
options (e.g. verbosity level), which should be specified first.
Do not mix input and output files -- first specify all input files,
then all output files. Also do not mix options which belong to
different files. All options apply ONLY to the next input or output
file and are reset between files.
· To set the video bitrate of the output file to 64kbit/s:
avconv-i input.avi -b 64k output.avi
· To force the frame rate of the output file to 24 fps:
avconv-i input.avi -r 24 output.avi
· To force the frame rate of the input file (valid for raw formats
only) to 1 fps and the frame rate of the output file to 24 fps:
avconv-r 1 -i input.m2v -r 24 output.avi
The format option may be needed for raw input files.
STREAM SELECTION
By default avconv tries to pick the "best" stream of each type present
in input files and add them to each output file. For video, this means
the highest resolution, for audio the highest channel count. For
subtitle it's simply the first subtitle stream.
You can disable some of those defaults by using "-vn/-an/-sn" options.
For full manual control, use the "-map" option, which disables the
defaults just described.
OPTIONS
All the numerical options, if not specified otherwise, accept in input
a string representing a number, which may contain one of the
International System number postfixes, for example 'K', 'M', 'G'. If
'i' is appended after the postfix, powers of 2 are used instead of
powers of 10. The 'B' postfix multiplies the value for 8, and can be
appended after another postfix or used alone. This allows using for
example 'KB', 'MiB', 'G' and 'B' as postfix.
Options which do not take arguments are boolean options, and set the
corresponding value to true. They can be set to false by prefixing with
"no" the option name, for example using "-nofoo" in the command line
will set to false the boolean option with name "foo".
Stream specifiers
Some options are applied per-stream, e.g. bitrate or codec. Stream
specifiers are used to precisely specify which stream(s) does a given
option belong to.
A stream specifier is a string generally appended to the option name
and separated from it by a colon. E.g. "-codec:a:1 ac3" option contains
"a:1" stream specifer, which matches the second audio stream. Therefore
it would select the ac3 codec for the second audio stream.
A stream specifier can match several stream, the option is then applied
to all of them. E.g. the stream specifier in "-b:a 128k" matches all
audio streams.
An empty stream specifier matches all streams, for example "-codec
copy" or "-codec: copy" would copy all the streams without reencoding.
Possible forms of stream specifiers are:
stream_index
Matches the stream with this index. E.g. "-threads:1 4" would set
the thread count for the second stream to 4.
stream_type[:stream_index]
stream_type is one of: 'v' for video, 'a' for audio, 's' for
subtitle, 'd' for data and 't' for attachments. If stream_index is
given, then matches stream number stream_index of this type.
Otherwise matches all streams of this type.
p:program_id[:stream_index]
If stream_index is given, then matches stream number stream_index
in program with id program_id. Otherwise matches all streams in
this program.
Generic options
These options are shared amongst the av* tools.
-L Show license.
-h, -?, -help, --help
Show help.
-version
Show version.
-formats
Show available formats.
The fields preceding the format names have the following meanings:
D Decoding available
E Encoding available
-codecs
Show available codecs.
The fields preceding the codec names have the following meanings:
D Decoding available
E Encoding available
V/A/S
Video/audio/subtitle codec
S Codec supports slices
D Codec supports direct rendering
T Codec can handle input truncated at random locations instead of
only at frame boundaries
-bsfs
Show available bitstream filters.
-protocols
Show available protocols.
-filters
Show available libavfilter filters.
-pix_fmts
Show available pixel formats.
-sample_fmts
Show available sample formats.
-loglevel loglevel | -v loglevel
Set the logging level used by the library. loglevel is a number or
a string containing one of the following values:
quiet
panic
fatal
error
warning
info
verbose
debug
By default the program logs to stderr, if coloring is supported by
the terminal, colors are used to mark errors and warnings. Log
coloring can be disabled setting the environment variable
AV_LOG_FORCE_NOCOLOR or NO_COLOR, or can be forced setting the
environment variable AV_LOG_FORCE_COLOR. The use of the
environment variable NO_COLOR is deprecated and will be dropped in
a following Libav version.
AVOptions
These options are provided directly by the libavformat, libavdevice and
libavcodec libraries. To see the list of available AVOptions, use the
-help option. They are separated into two categories:
generic
These options can be set for any container, codec or device.
Generic options are listed under AVFormatContext options for
containers/devices and under AVCodecContext options for codecs.
private
These options are specific to the given container, device or codec.
Private options are listed under their corresponding
containers/devices/codecs.
For example to write an ID3v2.3 header instead of a default ID3v2.4 to
an MP3 file, use the id3v2_version private option of the MP3 muxer:
avconv-i input.flac -id3v2_version 3 out.mp3
All codec AVOptions are obviously per-stream, so the chapter on stream
specifiers applies to them
Note -nooption syntax cannot be used for boolean AVOptions, use -option
0/-option 1.
Note2 old undocumented way of specifying per-stream AVOptions by
prepending v/a/s to the options name is now obsolete and will be
removed soon.
Main options
-f fmt (input/output)
Force input or output file format. The format is normally
autodetected for input files and guessed from file extension for
output files, so this option is not needed in most cases.
-i filename (input)
input file name
-y (global)
Overwrite output files without asking.
-c[:stream_specifier] codec (input/output,per-stream)
-codec[:stream_specifier] codec (input/output,per-stream)
Select an encoder (when used before an output file) or a decoder
(when used before an input file) for one or more streams. codec is
the name of a decoder/encoder or a special value "copy" (output
only) to indicate that the stream is not to be reencoded.
For example
avconv-i INPUT -map 0 -c:v libx264 -c:a copy OUTPUT
encodes all video streams with libx264 and copies all audio
streams.
For each stream, the last matching "c" option is applied, so
avconv-i INPUT -map 0 -c copy -c:v:1 libx264 -c:a:137 libvorbis OUTPUT
will copy all the streams except the second video, which will be
encoded with libx264, and the 138th audio, which will be encoded
with libvorbis.
-t duration (output)
Stop writing the output after its duration reaches duration.
duration may be a number in seconds, or in "hh:mm:ss[.xxx]" form.
-fs limit_size (output)
Set the file size limit.
-ss position (input/output)
When used as an input option (before "-i"), seeks in this input
file to position. When used as an output option (before an output
filename), decodes but discards input until the timestamps reach
position. This is slower, but more accurate.
position may be either in seconds or in "hh:mm:ss[.xxx]" form.
-itsoffset offset (input)
Set the input time offset in seconds. "[-]hh:mm:ss[.xxx]" syntax
is also supported. The offset is added to the timestamps of the
input files. Specifying a positive offset means that the
corresponding streams are delayed by offset seconds.
-metadata[:metadata_specifier] key=value (output,per-metadata)
Set a metadata key/value pair.
An optional metadata_specifier may be given to set metadata on
streams or chapters. See "-map_metadata" documentation for details.
This option overrides metadata set with "-map_metadata". It is also
possible to delete metadata by using an empty value.
For example, for setting the title in the output file:
avconv-i in.avi -metadata title="my title" out.flv
To set the language of the first audio stream:
avconv-i INPUT -metadata:s:a:0 language=eng OUTPUT
-target type (output)
Specify target file type ("vcd", "svcd", "dvd", "dv", "dv50"). type
may be prefixed with "pal-", "ntsc-" or "film-" to use the
corresponding standard. All the format options (bitrate, codecs,
buffer sizes) are then set automatically. You can just type:
avconv-i myfile.avi -target vcd /tmp/vcd.mpg
Nevertheless you can specify additional options as long as you know
they do not conflict with the standard, as in:
avconv-i myfile.avi -target vcd -bf 2 /tmp/vcd.mpg
-dframes number (output)
Set the number of data frames to record. This is an alias for
"-frames:d".
-frames[:stream_specifier] framecount (output,per-stream)
Stop writing to the stream after framecount frames.
-q[:stream_specifier] q (output,per-stream)
-qscale[:stream_specifier] q (output,per-stream)
Use fixed quality scale (VBR). The meaning of q is codec-dependent.
-filter[:stream_specifier] filter_graph (output,per-stream)
filter_graph is a description of the filter graph to apply to the
stream. Use "-filters" to show all the available filters (including
also sources and sinks).
-pre[:stream_specifier] preset_name (output,per-stream)
Specify the preset for matching stream(s).
-stats (global)
Print encoding progress/statistics. On by default.
-attach filename (output)
Add an attachment to the output file. This is supported by a few
formats like Matroska for e.g. fonts used in rendering subtitles.
Attachments are implemented as a specific type of stream, so this
option will add a new stream to the file. It is then possible to
use per-stream options on this stream in the usual way. Attachment
streams created with this option will be created after all the
other streams (i.e. those created with "-map" or automatic
mappings).
Note that for Matroska you also have to set the mimetype metadata
tag:
avconv-i INPUT -attach DejaVuSans.ttf -metadata:s:2 mimetype=application/x-truetype-font out.mkv
(assuming that the attachment stream will be third in the output
file).
-dump_attachment[:stream_specifier] filename (input,per-stream)
Extract the matching attachment stream into a file named filename.
If filename is empty, then the value of the "filename" metadata tag
will be used.
E.g. to extract the first attachment to a file named 'out.ttf':
avconv -dump_attachment:t:0 out.ttf INPUT
To extract all attachments to files determined by the "filename"
tag:
avconv -dump_attachment:t "" INPUT
Technical note -- attachments are implemented as codec extradata,
so this option can actually be used to extract extradata from any
stream, not just attachments.
Video Options
-vframes number (output)
Set the number of video frames to record. This is an alias for
"-frames:v".
-r[:stream_specifier] fps (input/output,per-stream)
Set frame rate (Hz value, fraction or abbreviation), (default =
25).
-s[:stream_specifier] size (input/output,per-stream)
Set frame size. The format is wxh (default - same as source). The
following abbreviations are recognized:
sqcif
128x96
qcif
176x144
cif 352x288
4cif
704x576
16cif
1408x1152
qqvga
160x120
qvga
320x240
vga 640x480
svga
800x600
xga 1024x768
uxga
1600x1200
qxga
2048x1536
sxga
1280x1024
qsxga
2560x2048
hsxga
5120x4096
wvga
852x480
wxga
1366x768
wsxga
1600x1024
wuxga
1920x1200
woxga
2560x1600
wqsxga
3200x2048
wquxga
3840x2400
whsxga
6400x4096
whuxga
7680x4800
cga 320x200
ega 640x350
hd480
852x480
hd720
1280x720
hd1080
1920x1080
-aspect[:stream_specifier] aspect (output,per-stream)
Set the video display aspect ratio specified by aspect.
aspect can be a floating point number string, or a string of the
form num:den, where num and den are the numerator and denominator
of the aspect ratio. For example "4:3", "16:9", "1.3333", and
"1.7777" are valid argument values.
-vn (output)
Disable video recording.
-bt tolerance
Set video bitrate tolerance (in bits, default 4000k). Has a
minimum value of: (target_bitrate/target_framerate). In 1-pass
mode, bitrate tolerance specifies how far ratecontrol is willing to
deviate from the target average bitrate value. This is not related
to min/max bitrate. Lowering tolerance too much has an adverse
effect on quality.
-maxrate bitrate
Set max video bitrate (in bit/s). Requires -bufsize to be set.
-minrate bitrate
Set min video bitrate (in bit/s). Most useful in setting up a CBR
encode:
avconv-i myfile.avi -b 4000k -minrate 4000k -maxrate 4000k -bufsize 1835k out.m2v
It is of little use elsewise.
-bufsize size
Set video buffer verifier buffer size (in bits).
-vcodec codec (output)
Set the video codec. This is an alias for "-codec:v".
-same_quant
Use same quantizer as source (implies VBR).
Note that this is NOT SAME QUALITY. Do not use this option unless
you know you need it.
-pass n
Select the pass number (1 or 2). It is used to do two-pass video
encoding. The statistics of the video are recorded in the first
pass into a log file (see also the option -passlogfile), and in the
second pass that log file is used to generate the video at the
exact requested bitrate. On pass 1, you may just deactivate audio
and set output to null, examples for Windows and Unix:
avconv-i foo.mov -c:v libxvid -pass 1 -an -f rawvideo -y NUL
avconv-i foo.mov -c:v libxvid -pass 1 -an -f rawvideo -y /dev/null
-passlogfile prefix (global)
Set two-pass log file name prefix to prefix, the default file name
prefix is ``av2pass''. The complete file name will be PREFIX-N.log,
where N is a number specific to the output stream.
-vf filter_graph (output)
filter_graph is a description of the filter graph to apply to the
input video. Use the option "-filters" to show all the available
filters (including also sources and sinks). This is an alias for
"-filter:v".
Advanced Video Options
-pix_fmt[:stream_specifier] format (input/output,per-stream)
Set pixel format. Use "-pix_fmts" to show all the supported pixel
formats.
-sws_flags flags (input/output)
Set SwScaler flags.
-g gop_size
Set the group of pictures size.
-vdt n
Discard threshold.
-qmin q
minimum video quantizer scale (VBR)
-qmax q
maximum video quantizer scale (VBR)
-qdiff q
maximum difference between the quantizer scales (VBR)
-qblur blur
video quantizer scale blur (VBR) (range 0.0 - 1.0)
-qcomp compression
video quantizer scale compression (VBR) (default 0.5). Constant of
ratecontrol equation. Recommended range for default rc_eq: 0.0-1.0
-lmin lambda
minimum video lagrange factor (VBR)
-lmax lambda
max video lagrange factor (VBR)
-mblmin lambda
minimum macroblock quantizer scale (VBR)
-mblmax lambda
maximum macroblock quantizer scale (VBR)
These four options (lmin, lmax, mblmin, mblmax) use 'lambda' units,
but you may use the QP2LAMBDA constant to easily convert from 'q'
units:
avconv-i src.ext -lmax 21*QP2LAMBDA dst.ext
-rc_init_cplx complexity
initial complexity for single pass encoding
-b_qfactor factor
qp factor between P- and B-frames
-i_qfactor factor
qp factor between P- and I-frames
-b_qoffset offset
qp offset between P- and B-frames
-i_qoffset offset
qp offset between P- and I-frames
-rc_eq equation
Set rate control equation (see section "Expression Evaluation")
(default = "tex^qComp").
When computing the rate control equation expression, besides the
standard functions defined in the section "Expression Evaluation",
the following functions are available:
bits2qp(bits)qp2bits(qp)
and the following constants are available:
iTex
pTex
tex
mv
fCode
iCount
mcVar
var
isI
isP
isB
avgQP
qComp
avgIITex
avgPITex
avgPPTex
avgBPTex
avgTex
-rc_override[:stream_specifier] override (output,per-stream)
rate control override for specific intervals
-me_method method
Set motion estimation method to method. Available methods are
(from lowest to best quality):
zero
Try just the (0, 0) vector.
phods
log
x1
hex
umh
epzs
(default method)
full
exhaustive search (slow and marginally better than epzs)
-er n
Set error resilience to n.
1 FF_ER_CAREFUL (default)
2 FF_ER_COMPLIANT
3 FF_ER_AGGRESSIVE
4 FF_ER_VERY_AGGRESSIVE
-ec bit_mask
Set error concealment to bit_mask. bit_mask is a bit mask of the
following values:
1 FF_EC_GUESS_MVS (default = enabled)
2 FF_EC_DEBLOCK (default = enabled)
-bf frames
Use 'frames' B-frames (supported for MPEG-1, MPEG-2 and MPEG-4).
-mbd mode
macroblock decision
0 FF_MB_DECISION_SIMPLE: Use mb_cmp (cannot change it yet in
avconv).
1 FF_MB_DECISION_BITS: Choose the one which needs the fewest
bits.
2 FF_MB_DECISION_RD: rate distortion
-bug param
Work around encoder bugs that are not auto-detected.
-strict strictness
How strictly to follow the standards.
-deinterlace
Deinterlace pictures.
-vstats
Dump video coding statistics to vstats_HHMMSS.log.
-vstats_file file
Dump video coding statistics to file.
-top[:stream_specifier] n (output,per-stream)
top=1/bottom=0/auto=-1 field first
-dc precision
Intra_dc_precision.
-vtag fourcc/tag (output)
Force video tag/fourcc. This is an alias for "-tag:v".
-qphist (global)
Show QP histogram.
-force_key_frames[:stream_specifier] time[,time...] (output,per-stream)
Force key frames at the specified timestamps, more precisely at the
first frames after each specified time. This option can be useful
to ensure that a seek point is present at a chapter mark or any
other designated place in the output file. The timestamps must be
specified in ascending order.
-copyinkf[:stream_specifier] (output,per-stream)
When doing stream copy, copy also non-key frames found at the
beginning.
Audio Options
-aframes number (output)
Set the number of audio frames to record. This is an alias for
"-frames:a".
-ar[:stream_specifier] freq (input/output,per-stream)
Set the audio sampling frequency. For output streams it is set by
default to the frequency of the corresponding input stream. For
input streams this option only makes sense for audio grabbing
devices and raw demuxers and is mapped to the corresponding demuxer
options.
-aq q (output)
Set the audio quality (codec-specific, VBR). This is an alias for
-q:a.
-ac[:stream_specifier] channels (input/output,per-stream)
Set the number of audio channels. For output streams it is set by
default to the number of input audio channels. For input streams
this option only makes sense for audio grabbing devices and raw
demuxers and is mapped to the corresponding demuxer options.
-an (output)
Disable audio recording.
-acodec codec (input/output)
Set the audio codec. This is an alias for "-codec:a".
-sample_fmt[:stream_specifier] sample_fmt (output,per-stream)
Set the audio sample format. Use "-sample_fmts" to get a list of
supported sample formats.
Advanced Audio options:
-atag fourcc/tag (output)
Force audio tag/fourcc. This is an alias for "-tag:a".
-audio_service_type type
Set the type of service that the audio stream contains.
ma Main Audio Service (default)
ef Effects
vi Visually Impaired
hi Hearing Impaired
di Dialogue
co Commentary
em Emergency
vo Voice Over
ka Karaoke
Subtitle options:
-scodec codec (input/output)
Set the subtitle codec. This is an alias for "-codec:s".
-sn (output)
Disable subtitle recording.
Audio/Video grab options
-isync (global)
Synchronize read on input.
Advanced options
-map
[-]input_file_id[:stream_specifier][,sync_file_id[:stream_specifier]]
(output)
Designate one or more input streams as a source for the output
file. Each input stream is identified by the input file index
input_file_id and the input stream index input_stream_id within the
input file. Both indices start at 0. If specified,
sync_file_id:stream_specifier sets which input stream is used as a
presentation sync reference.
The first "-map" option on the command line specifies the source
for output stream 0, the second "-map" option specifies the source
for output stream 1, etc.
A "-" character before the stream identifier creates a "negative"
mapping. It disables matching streams from already created
mappings.
For example, to map ALL streams from the first input file to output
avconv-i INPUT -map 0 output
For example, if you have two audio streams in the first input file,
these streams are identified by "0:0" and "0:1". You can use "-map"
to select which streams to place in an output file. For example:
avconv-i INPUT -map 0:1 out.wav
will map the input stream in INPUT identified by "0:1" to the
(single) output stream in out.wav.
For example, to select the stream with index 2 from input file
a.mov (specified by the identifier "0:2"), and stream with index 6
from input b.mov (specified by the identifier "1:6"), and copy them
to the output file out.mov:
avconv-i a.mov -i b.mov -c copy -map 0:2 -map 1:6 out.mov
To select all video and the third audio stream from an input file:
avconv-i INPUT -map 0:v -map 0:a:2 OUTPUT
To map all the streams except the second audio, use negative
mappings
avconv-i INPUT -map 0 -map -0:a:1 OUTPUT
Note that using this option disables the default mappings for this
output file.
-map_metadata[:metadata_spec_out] infile[:metadata_spec_in]
(output,per-metadata)
Set metadata information of the next output file from infile. Note
that those are file indices (zero-based), not filenames. Optional
metadata_spec_in/out parameters specify, which metadata to copy. A
metadata specifier can have the following forms:
g global metadata, i.e. metadata that applies to the whole file
s[:stream_spec]
per-stream metadata. stream_spec is a stream specifier as
described in the Stream specifiers chapter. In an input
metadata specifier, the first matching stream is copied from.
In an output metadata specifier, all matching streams are
copied to.
c:chapter_index
per-chapter metadata. chapter_index is the zero-based chapter
index.
p:program_index
per-program metadata. program_index is the zero-based program
index.
If metadata specifier is omitted, it defaults to global.
By default, global metadata is copied from the first input file,
per-stream and per-chapter metadata is copied along with
streams/chapters. These default mappings are disabled by creating
any mapping of the relevant type. A negative file index can be used
to create a dummy mapping that just disables automatic copying.
For example to copy metadata from the first stream of the input
file to global metadata of the output file:
avconv-i in.ogg -map_metadata 0:s:0 out.mp3
To do the reverse, i.e. copy global metadata to all audio streams:
avconv-i in.mkv -map_metadata:s:a 0:g out.mkv
Note that simple 0 would work as well in this example, since global
metadata is assumed by default.
-map_chapters input_file_index (output)
Copy chapters from input file with index input_file_index to the
next output file. If no chapter mapping is specified, then chapters
are copied from the first input file with at least one chapter. Use
a negative file index to disable any chapter copying.
-debug
Print specific debug info.
-benchmark (global)
Show benchmarking information at the end of an encode. Shows CPU
time used and maximum memory consumption. Maximum memory
consumption is not supported on all systems, it will usually
display as 0 if not supported.
-timelimit duration (global)
Exit after avconv has been running for duration seconds.
-dump (global)
Dump each input packet to stderr.
-hex (global)
When dumping packets, also dump the payload.
-ps size
Set RTP payload size in bytes.
-re (input)
Read input at native frame rate. Mainly used to simulate a grab
device.
-threads count
Thread count.
-vsync parameter
Video sync method.
passthrough
Each frame is passed with its timestamp from the demuxer to the
muxer.
cfr Frames will be duplicated and dropped to achieve exactly the
requested constant framerate.
vfr Frames are passed through with their timestamp or dropped so as
to prevent 2 frames from having the same timestamp.
auto
Chooses between 1 and 2 depending on muxer capabilities. This
is the default method.
With -map you can select from which stream the timestamps should be
taken. You can leave either video or audio unchanged and sync the
remaining stream(s) to the unchanged one.
-async samples_per_second
Audio sync method. "Stretches/squeezes" the audio stream to match
the timestamps, the parameter is the maximum samples per second by
which the audio is changed. -async 1 is a special case where only
the start of the audio stream is corrected without any later
correction.
-copyts
Copy timestamps from input to output.
-copytb
Copy input stream time base from input to output when stream
copying.
-shortest
Finish encoding when the shortest input stream ends.
-dts_delta_threshold
Timestamp discontinuity delta threshold.
-muxdelay seconds (input)
Set the maximum demux-decode delay.
-muxpreload seconds (input)
Set the initial demux-decode delay.
-streamid output-stream-index:new-value (output)
Assign a new stream-id value to an output stream. This option
should be specified prior to the output filename to which it
applies. For the situation where multiple output files exist, a
streamid may be reassigned to a different value.
For example, to set the stream 0 PID to 33 and the stream 1 PID to
36 for an output mpegts file:
avconv-i infile -streamid 0:33 -streamid 1:36 out.ts
-bsf[:stream_specifier] bitstream_filters (output,per-stream)
Set bitstream filters for matching streams. bistream_filters is a
comma-separated list of bitstream filters. Use the "-bsfs" option
to get the list of bitstream filters.
avconv-i h264.mp4 -c:v copy -vbsf h264_mp4toannexb -an out.h264
avconv-i file.mov -an -vn -sbsf mov2textsub -c:s copy -f rawvideo sub.txt
-tag[:stream_specifier] codec_tag (output,per-stream)
Force a tag/fourcc for matching streams.
TIPS
· For streaming at very low bitrate application, use a low frame rate
and a small GOP size. This is especially true for RealVideo where
the Linux player does not seem to be very fast, so it can miss
frames. An example is:
avconv-g 3 -r 3 -t 10 -b 50k -s qcif -f rv10 /tmp/b.rm
· The parameter 'q' which is displayed while encoding is the current
quantizer. The value 1 indicates that a very good quality could be
achieved. The value 31 indicates the worst quality. If q=31 appears
too often, it means that the encoder cannot compress enough to meet
your bitrate. You must either increase the bitrate, decrease the
frame rate or decrease the frame size.
· If your computer is not fast enough, you can speed up the
compression at the expense of the compression ratio. You can use
'-me zero' to speed up motion estimation, and '-intra' to disable
motion estimation completely (you have only I-frames, which means
it is about as good as JPEG compression).
· To have very low audio bitrates, reduce the sampling frequency
(down to 22050 Hz for MPEG audio, 22050 or 11025 for AC-3).
· To have a constant quality (but a variable bitrate), use the option
'-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst
quality).
EXAMPLES
Preset files
A preset file contains a sequence of option=value pairs, one for each
line, specifying a sequence of options which can be specified also on
the command line. Lines starting with the hash ('#') character are
ignored and are used to provide comments. Empty lines are also ignored.
Check the presets directory in the Libav source tree for examples.
Preset files are specified with the "pre" option, this option takes a
preset name as input. Avconv searches for a file named
preset_name.avpreset in the directories $AVCONV_DATADIR (if set), and
$HOME/.avconv, and in the data directory defined at configuration time
(usually $PREFIX/share/avconv) in that order. For example, if the
argument is "libx264-max", it will search for the file
libx264-max.avpreset.
Video and Audio grabbing
If you specify the input format and device then avconv can grab video
and audio directly.
avconv-f oss -i /dev/dsp -f video4linux2 -i /dev/video0 /tmp/out.mpg
Note that you must activate the right video source and channel before
launching avconv with any TV viewer such as
xawtv ("http://linux.bytesex.org/xawtv/") by Gerd Knorr. You also have
to set the audio recording levels correctly with a standard mixer.
X11 grabbing
Grab the X11 display with avconv via
avconv-f x11grab -s cif -r 25 -i :0.0 /tmp/out.mpg
0.0 is display.screen number of your X11 server, same as the DISPLAY
environment variable.
avconv-f x11grab -s cif -r 25 -i :0.0+10,20 /tmp/out.mpg
0.0 is display.screen number of your X11 server, same as the DISPLAY
environment variable. 10 is the x-offset and 20 the y-offset for the
grabbing.
Video and Audio file format conversion
Any supported file format and protocol can serve as input to avconv:
Examples:
· You can use YUV files as input:
avconv-i /tmp/test%d.Y /tmp/out.mpg
It will use the files:
/tmp/test0.Y, /tmp/test0.U, /tmp/test0.V,
/tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc...
The Y files use twice the resolution of the U and V files. They are
raw files, without header. They can be generated by all decent
video decoders. You must specify the size of the image with the -s
option if avconv cannot guess it.
· You can input from a raw YUV420P file:
avconv-i /tmp/test.yuv /tmp/out.avi
test.yuv is a file containing raw YUV planar data. Each frame is
composed of the Y plane followed by the U and V planes at half
vertical and horizontal resolution.
· You can output to a raw YUV420P file:
avconv-i mydivx.avi hugefile.yuv
· You can set several input files and output files:
avconv-i /tmp/a.wav -s 640x480 -i /tmp/a.yuv /tmp/a.mpg
Converts the audio file a.wav and the raw YUV video file a.yuv to
MPEG file a.mpg.
· You can also do audio and video conversions at the same time:
avconv-i /tmp/a.wav -ar 22050 /tmp/a.mp2
Converts a.wav to MPEG audio at 22050 Hz sample rate.
· You can encode to several formats at the same time and define a
mapping from input stream to output streams:
avconv-i /tmp/a.wav -map 0:a -b 64k /tmp/a.mp2 -map 0:a -b 128k /tmp/b.mp2
Converts a.wav to a.mp2 at 64 kbits and to b.mp2 at 128 kbits.
'-map file:index' specifies which input stream is used for each
output stream, in the order of the definition of output streams.
· You can transcode decrypted VOBs:
avconv-i snatch_1.vob -f avi -c:v mpeg4 -b:v 800k -g 300 -bf 2 -c:a libmp3lame -b:a 128k snatch.avi
This is a typical DVD ripping example; the input is a VOB file, the
output an AVI file with MPEG-4 video and MP3 audio. Note that in
this command we use B-frames so the MPEG-4 stream is DivX5
compatible, and GOP size is 300 which means one intra frame every
10 seconds for 29.97fps input video. Furthermore, the audio stream
is MP3-encoded so you need to enable LAME support by passing
"--enable-libmp3lame" to configure. The mapping is particularly
useful for DVD transcoding to get the desired audio language.
NOTE: To see the supported input formats, use "avconv -formats".
· You can extract images from a video, or create a video from many
images:
For extracting images from a video:
avconv-i foo.avi -r 1 -s WxH -f image2 foo-%03d.jpeg
This will extract one video frame per second from the video and
will output them in files named foo-001.jpeg, foo-002.jpeg, etc.
Images will be rescaled to fit the new WxH values.
If you want to extract just a limited number of frames, you can use
the above command in combination with the -vframes or -t option, or
in combination with -ss to start extracting from a certain point in
time.
For creating a video from many images:
avconv-f image2 -i foo-%03d.jpeg -r 12 -s WxH foo.avi
The syntax "foo-%03d.jpeg" specifies to use a decimal number
composed of three digits padded with zeroes to express the sequence
number. It is the same syntax supported by the C printf function,
but only formats accepting a normal integer are suitable.
· You can put many streams of the same type in the output:
avconv-i test1.avi -i test2.avi -map 0.3 -map 0.2 -map 0.1 -map 0.0 -c copy test12.nut
The resulting output file test12.avi will contain first four
streams from the input file in reverse order.
EXPRESSION EVALUATION
When evaluating an arithmetic expression, Libav uses an internal
formula evaluator, implemented through the libavutil/eval.h interface.
An expression may contain unary, binary operators, constants, and
functions.
Two expressions expr1 and expr2 can be combined to form another
expression "expr1;expr2". expr1 and expr2 are evaluated in turn, and
the new expression evaluates to the value of expr2.
The following binary operators are available: "+", "-", "*", "/", "^".
The following unary operators are available: "+", "-".
The following functions are available:
sinh(x)cosh(x)tanh(x)sin(x)cos(x)tan(x)atan(x)asin(x)acos(x)exp(x)log(x)abs(x)squish(x)gauss(x)isnan(x)
Return 1.0 if x is NAN, 0.0 otherwise.
mod(x, y)
max(x, y)
min(x, y)
eq(x, y)
gte(x, y)
gt(x, y)
lte(x, y)
lt(x, y)
st(var, expr)
Allow to store the value of the expression expr in an internal
variable. var specifies the number of the variable where to store
the value, and it is a value ranging from 0 to 9. The function
returns the value stored in the internal variable.
ld(var)
Allow to load the value of the internal variable with number var,
which was previously stored with st(var, expr). The function
returns the loaded value.
while(cond, expr)
Evaluate expression expr while the expression cond is non-zero, and
returns the value of the last expr evaluation, or NAN if cond was
always false.
ceil(expr)
Round the value of expression expr upwards to the nearest integer.
For example, "ceil(1.5)" is "2.0".
floor(expr)
Round the value of expression expr downwards to the nearest
integer. For example, "floor(-1.5)" is "-2.0".
trunc(expr)
Round the value of expression expr towards zero to the nearest
integer. For example, "trunc(-1.5)" is "-1.0".
sqrt(expr)
Compute the square root of expr. This is equivalent to "(expr)^.5".
not(expr)
Return 1.0 if expr is zero, 0.0 otherwise.
Note that:
"*" works like AND
"+" works like OR
thus
if A then B else C
is equivalent to
A*B + not(A)*C
In your C code, you can extend the list of unary and binary functions,
and define recognized constants, so that they are available for your
expressions.
The evaluator also recognizes the International System number
postfixes. If 'i' is appended after the postfix, powers of 2 are used
instead of powers of 10. The 'B' postfix multiplies the value for 8,
and can be appended after another postfix or used alone. This allows
using for example 'KB', 'MiB', 'G' and 'B' as postfix.
Follows the list of available International System postfixes, with
indication of the corresponding powers of 10 and of 2.
y -24 / -80
z -21 / -70
a -18 / -60
f -15 / -50
p -12 / -40
n -9 / -30
u -6 / -20
m -3 / -10
c -2
d -1
h 2
k 3 / 10
K 3 / 10
M 6 / 20
G 9 / 30
T 12 / 40
P 15 / 40
E 18 / 50
Z 21 / 60
Y 24 / 70
ENCODERS
Encoders are configured elements in Libav which allow the encoding of
multimedia streams.
When you configure your Libav build, all the supported native encoders
are enabled by default. Encoders requiring an external library must be
enabled manually via the corresponding "--enable-lib" option. You can
list all available encoders using the configure option
"--list-encoders".
You can disable all the encoders with the configure option
"--disable-encoders" and selectively enable / disable single encoders
with the options "--enable-encoder=ENCODER" /
"--disable-encoder=ENCODER".
The option "-codecs" of the av* tools will display the list of enabled
encoders.
AUDIO ENCODERS
A description of some of the currently available audio encoders
follows.
ac3 and ac3_fixed
AC-3 audio encoders.
These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as
well as the undocumented RealAudio 3 (a.k.a. dnet).
The ac3 encoder uses floating-point math, while the ac3_fixed encoder
only uses fixed-point integer math. This does not mean that one is
always faster, just that one or the other may be better suited to a
particular system. The floating-point encoder will generally produce
better quality audio for a given bitrate. The ac3_fixed encoder is not
the default codec for any of the output formats, so it must be
specified explicitly using the option "-acodec ac3_fixed" in order to
use it.
AC-3 Metadata
The AC-3 metadata options are used to set parameters that describe the
audio, but in most cases do not affect the audio encoding itself. Some
of the options do directly affect or influence the decoding and
playback of the resulting bitstream, while others are just for
informational purposes. A few of the options will add bits to the
output stream that could otherwise be used for audio data, and will
thus affect the quality of the output. Those will be indicated
accordingly with a note in the option list below.
These parameters are described in detail in several publicly-available
documents.
*<A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard
("http://www.atsc.org/cms/standards/a_52-2010.pdf")>
*<A/54 - Guide to the Use of the ATSC Digital Television Standard
("http://www.atsc.org/cms/standards/a_54a_with_corr_1.pdf")>
*<Dolby Metadata Guide
("http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf")>
*<Dolby Digital Professional Encoding Guidelines
("http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf")>
Metadata Control Options
-per_frame_metadata boolean
Allow Per-Frame Metadata. Specifies if the encoder should check for
changing metadata for each frame.
0 The metadata values set at initialization will be used for
every frame in the stream. (default)
1 Metadata values can be changed before encoding each frame.
Downmix Levels
-center_mixlev level
Center Mix Level. The amount of gain the decoder should apply to
the center channel when downmixing to stereo. This field will only
be written to the bitstream if a center channel is present. The
value is specified as a scale factor. There are 3 valid values:
0.707
Apply -3dB gain
0.595
Apply -4.5dB gain (default)
0.500
Apply -6dB gain
-surround_mixlev level
Surround Mix Level. The amount of gain the decoder should apply to
the surround channel(s) when downmixing to stereo. This field will
only be written to the bitstream if one or more surround channels
are present. The value is specified as a scale factor. There are 3
valid values:
0.707
Apply -3dB gain
0.500
Apply -6dB gain (default)
0.000
Silence Surround Channel(s)
Audio Production Information
Audio Production Information is optional information describing the
mixing environment. Either none or both of the fields are written to
the bitstream.
-mixing_level number
Mixing Level. Specifies peak sound pressure level (SPL) in the
production environment when the mix was mastered. Valid values are
80 to 111, or -1 for unknown or not indicated. The default value is
-1, but that value cannot be used if the Audio Production
Information is written to the bitstream. Therefore, if the
"room_type" option is not the default value, the "mixing_level"
option must not be -1.
-room_type type
Room Type. Describes the equalization used during the final mixing
session at the studio or on the dubbing stage. A large room is a
dubbing stage with the industry standard X-curve equalization; a
small room has flat equalization. This field will not be written
to the bitstream if both the "mixing_level" option and the
"room_type" option have the default values.
0
notindicated
Not Indicated (default)
1
large
Large Room
2
small
Small Room
Other Metadata Options
-copyright boolean
Copyright Indicator. Specifies whether a copyright exists for this
audio.
0
off No Copyright Exists (default)
1
on Copyright Exists
-dialnorm value
Dialogue Normalization. Indicates how far the average dialogue
level of the program is below digital 100% full scale (0 dBFS).
This parameter determines a level shift during audio reproduction
that sets the average volume of the dialogue to a preset level. The
goal is to match volume level between program sources. A value of
-31dB will result in no volume level change, relative to the source
volume, during audio reproduction. Valid values are whole numbers
in the range -31 to -1, with -31 being the default.
-dsur_mode mode
Dolby Surround Mode. Specifies whether the stereo signal uses Dolby
Surround (Pro Logic). This field will only be written to the
bitstream if the audio stream is stereo. Using this option does NOT
mean the encoder will actually apply Dolby Surround processing.
0
notindicated
Not Indicated (default)
1
off Not Dolby Surround Encoded
2
on Dolby Surround Encoded
-original boolean
Original Bit Stream Indicator. Specifies whether this audio is from
the original source and not a copy.
0
off Not Original Source
1
on Original Source (default)
Extended Bitstream Information
The extended bitstream options are part of the Alternate Bit Stream
Syntax as specified in Annex D of the A/52:2010 standard. It is grouped
into 2 parts. If any one parameter in a group is specified, all values
in that group will be written to the bitstream. Default values are
used for those that are written but have not been specified. If the
mixing levels are written, the decoder will use these values instead of
the ones specified in the "center_mixlev" and "surround_mixlev" options
if it supports the Alternate Bit Stream Syntax.
Extended Bitstream Information - Part 1
-dmix_mode mode
Preferred Stereo Downmix Mode. Allows the user to select either
Lt/Rt (Dolby Surround) or Lo/Ro (normal stereo) as the preferred
stereo downmix mode.
0
notindicated
Not Indicated (default)
1
ltrt
Lt/Rt Downmix Preferred
2
loro
Lo/Ro Downmix Preferred
-ltrt_cmixlev level
Lt/Rt Center Mix Level. The amount of gain the decoder should apply
to the center channel when downmixing to stereo in Lt/Rt mode.
1.414
Apply +3dB gain
1.189
Apply +1.5dB gain
1.000
Apply 0dB gain
0.841
Apply -1.5dB gain
0.707
Apply -3.0dB gain
0.595
Apply -4.5dB gain (default)
0.500
Apply -6.0dB gain
0.000
Silence Center Channel
-ltrt_surmixlev level
Lt/Rt Surround Mix Level. The amount of gain the decoder should
apply to the surround channel(s) when downmixing to stereo in Lt/Rt
mode.
0.841
Apply -1.5dB gain
0.707
Apply -3.0dB gain
0.595
Apply -4.5dB gain
0.500
Apply -6.0dB gain (default)
0.000
Silence Surround Channel(s)-loro_cmixlev level
Lo/Ro Center Mix Level. The amount of gain the decoder should apply
to the center channel when downmixing to stereo in Lo/Ro mode.
1.414
Apply +3dB gain
1.189
Apply +1.5dB gain
1.000
Apply 0dB gain
0.841
Apply -1.5dB gain
0.707
Apply -3.0dB gain
0.595
Apply -4.5dB gain (default)
0.500
Apply -6.0dB gain
0.000
Silence Center Channel
-loro_surmixlev level
Lo/Ro Surround Mix Level. The amount of gain the decoder should
apply to the surround channel(s) when downmixing to stereo in Lo/Ro
mode.
0.841
Apply -1.5dB gain
0.707
Apply -3.0dB gain
0.595
Apply -4.5dB gain
0.500
Apply -6.0dB gain (default)
0.000
Silence Surround Channel(s)
Extended Bitstream Information - Part 2
-dsurex_mode mode
Dolby Surround EX Mode. Indicates whether the stream uses Dolby
Surround EX (7.1 matrixed to 5.1). Using this option does NOT mean
the encoder will actually apply Dolby Surround EX processing.
0
notindicated
Not Indicated (default)
1
on Dolby Surround EX Off
2
off Dolby Surround EX On
-dheadphone_mode mode
Dolby Headphone Mode. Indicates whether the stream uses Dolby
Headphone encoding (multi-channel matrixed to 2.0 for use with
headphones). Using this option does NOT mean the encoder will
actually apply Dolby Headphone processing.
0
notindicated
Not Indicated (default)
1
on Dolby Headphone Off
2
off Dolby Headphone On
-ad_conv_type type
A/D Converter Type. Indicates whether the audio has passed through
HDCD A/D conversion.
0
standard
Standard A/D Converter (default)
1
hdcd
HDCD A/D Converter
Other AC-3 Encoding Options
-stereo_rematrixing boolean
Stereo Rematrixing. Enables/Disables use of rematrixing for stereo
input. This is an optional AC-3 feature that increases quality by
selectively encoding the left/right channels as mid/side. This
option is enabled by default, and it is highly recommended that it
be left as enabled except for testing purposes.
Floating-Point-Only AC-3 Encoding Options
These options are only valid for the floating-point encoder and do not
exist for the fixed-point encoder due to the corresponding features not
being implemented in fixed-point.
-channel_coupling boolean
Enables/Disables use of channel coupling, which is an optional AC-3
feature that increases quality by combining high frequency
information from multiple channels into a single channel. The per-
channel high frequency information is sent with less accuracy in
both the frequency and time domains. This allows more bits to be
used for lower frequencies while preserving enough information to
reconstruct the high frequencies. This option is enabled by default
for the floating-point encoder and should generally be left as
enabled except for testing purposes or to increase encoding speed.
-1
auto
Selected by Encoder (default)
0
off Disable Channel Coupling
1
on Enable Channel Coupling
-cpl_start_band number
Coupling Start Band. Sets the channel coupling start band, from 1
to 15. If a value higher than the bandwidth is used, it will be
reduced to 1 less than the coupling end band. If auto is used, the
start band will be determined by the encoder based on the bit rate,
sample rate, and channel layout. This option has no effect if
channel coupling is disabled.
-1
auto
Selected by Encoder (default)
DEMUXERS
Demuxers are configured elements in Libav which allow to read the
multimedia streams from a particular type of file.
When you configure your Libav build, all the supported demuxers are
enabled by default. You can list all available ones using the configure
option "--list-demuxers".
You can disable all the demuxers using the configure option
"--disable-demuxers", and selectively enable a single demuxer with the
option "--enable-demuxer=DEMUXER", or disable it with the option
"--disable-demuxer=DEMUXER".
The option "-formats" of the av* tools will display the list of enabled
demuxers.
The description of some of the currently available demuxers follows.
image2
Image file demuxer.
This demuxer reads from a list of image files specified by a pattern.
The pattern may contain the string "%d" or "%0Nd", which specifies the
position of the characters representing a sequential number in each
filename matched by the pattern. If the form "%d0Nd" is used, the
string representing the number in each filename is 0-padded and N is
the total number of 0-padded digits representing the number. The
literal character '%' can be specified in the pattern with the string
"%%".
If the pattern contains "%d" or "%0Nd", the first filename of the file
list specified by the pattern must contain a number inclusively
contained between 0 and 4, all the following numbers must be
sequential. This limitation may be hopefully fixed.
The pattern may contain a suffix which is used to automatically
determine the format of the images contained in the files.
For example the pattern "img-%03d.bmp" will match a sequence of
filenames of the form img-001.bmp, img-002.bmp, ..., img-010.bmp, etc.;
the pattern "i%%m%%g-%d.jpg" will match a sequence of filenames of the
form i%m%g-1.jpg, i%m%g-2.jpg, ..., i%m%g-10.jpg, etc.
The size, the pixel format, and the format of each image must be the
same for all the files in the sequence.
The following example shows how to use avconv for creating a video from
the images in the file sequence img-001.jpeg, img-002.jpeg, ...,
assuming an input framerate of 10 frames per second:
avconv-i 'img-%03d.jpeg' -r 10 out.mkv
Note that the pattern must not necessarily contain "%d" or "%0Nd", for
example to convert a single image file img.jpeg you can employ the
command:
avconv-i img.jpeg img.png
applehttp
Apple HTTP Live Streaming demuxer.
This demuxer presents all AVStreams from all variant streams. The id
field is set to the bitrate variant index number. By setting the
discard flags on AVStreams (by pressing 'a' or 'v' in avplay), the
caller can decide which variant streams to actually receive. The total
bitrate of the variant that the stream belongs to is available in a
metadata key named "variant_bitrate".
MUXERS
Muxers are configured elements in Libav which allow writing multimedia
streams to a particular type of file.
When you configure your Libav build, all the supported muxers are
enabled by default. You can list all available muxers using the
configure option "--list-muxers".
You can disable all the muxers with the configure option
"--disable-muxers" and selectively enable / disable single muxers with
the options "--enable-muxer=MUXER" / "--disable-muxer=MUXER".
The option "-formats" of the av* tools will display the list of enabled
muxers.
A description of some of the currently available muxers follows.
crc
CRC (Cyclic Redundancy Check) testing format.
This muxer computes and prints the Adler-32 CRC of all the input audio
and video frames. By default audio frames are converted to signed
16-bit raw audio and video frames to raw video before computing the
CRC.
The output of the muxer consists of a single line of the form:
CRC=0xCRC, where CRC is a hexadecimal number 0-padded to 8 digits
containing the CRC for all the decoded input frames.
For example to compute the CRC of the input, and store it in the file
out.crc:
avconv-i INPUT -f crc out.crc
You can print the CRC to stdout with the command:
avconv-i INPUT -f crc -
You can select the output format of each frame with avconv by
specifying the audio and video codec and format. For example to compute
the CRC of the input audio converted to PCM unsigned 8-bit and the
input video converted to MPEG-2 video, use the command:
avconv-i INPUT -c:a pcm_u8 -c:v mpeg2video -f crc -
See also the framecrc muxer.
framecrc
Per-frame CRC (Cyclic Redundancy Check) testing format.
This muxer computes and prints the Adler-32 CRC for each decoded audio
and video frame. By default audio frames are converted to signed 16-bit
raw audio and video frames to raw video before computing the CRC.
The output of the muxer consists of a line for each audio and video
frame of the form: stream_index, frame_dts, frame_size, 0xCRC, where
CRC is a hexadecimal number 0-padded to 8 digits containing the CRC of
the decoded frame.
For example to compute the CRC of each decoded frame in the input, and
store it in the file out.crc:
avconv-i INPUT -f framecrc out.crc
You can print the CRC of each decoded frame to stdout with the command:
avconv-i INPUT -f framecrc -
You can select the output format of each frame with avconv by
specifying the audio and video codec and format. For example, to
compute the CRC of each decoded input audio frame converted to PCM
unsigned 8-bit and of each decoded input video frame converted to
MPEG-2 video, use the command:
avconv-i INPUT -c:a pcm_u8 -c:v mpeg2video -f framecrc -
See also the crc muxer.
image2
Image file muxer.
The image file muxer writes video frames to image files.
The output filenames are specified by a pattern, which can be used to
produce sequentially numbered series of files. The pattern may contain
the string "%d" or "%0Nd", this string specifies the position of the
characters representing a numbering in the filenames. If the form
"%0Nd" is used, the string representing the number in each filename is
0-padded to N digits. The literal character '%' can be specified in the
pattern with the string "%%".
If the pattern contains "%d" or "%0Nd", the first filename of the file
list specified will contain the number 1, all the following numbers
will be sequential.
The pattern may contain a suffix which is used to automatically
determine the format of the image files to write.
For example the pattern "img-%03d.bmp" will specify a sequence of
filenames of the form img-001.bmp, img-002.bmp, ..., img-010.bmp, etc.
The pattern "img%%-%d.jpg" will specify a sequence of filenames of the
form img%-1.jpg, img%-2.jpg, ..., img%-10.jpg, etc.
The following example shows how to use avconv for creating a sequence
of files img-001.jpeg, img-002.jpeg, ..., taking one image every second
from the input video:
avconv-i in.avi -vsync 1 -r 1 -f image2 'img-%03d.jpeg'
Note that with avconv, if the format is not specified with the "-f"
option and the output filename specifies an image file format, the
image2 muxer is automatically selected, so the previous command can be
written as:
avconv-i in.avi -vsync 1 -r 1 'img-%03d.jpeg'
Note also that the pattern must not necessarily contain "%d" or "%0Nd",
for example to create a single image file img.jpeg from the input video
you can employ the command:
avconv-i in.avi -f image2 -frames:v 1 img.jpeg
mpegts
MPEG transport stream muxer.
This muxer implements ISO 13818-1 and part of ETSI EN 300 468.
The muxer options are:
-mpegts_original_network_id number
Set the original_network_id (default 0x0001). This is unique
identifier of a network in DVB. Its main use is in the unique
identification of a service through the path Original_Network_ID,
Transport_Stream_ID.
-mpegts_transport_stream_id number
Set the transport_stream_id (default 0x0001). This identifies a
transponder in DVB.
-mpegts_service_id number
Set the service_id (default 0x0001) also known as program in DVB.
-mpegts_pmt_start_pid number
Set the first PID for PMT (default 0x1000, max 0x1f00).
-mpegts_start_pid number
Set the first PID for data packets (default 0x0100, max 0x0f00).
The recognized metadata settings in mpegts muxer are "service_provider"
and "service_name". If they are not set the default for
"service_provider" is "Libav" and the default for "service_name" is
"Service01".
avconv-i file.mpg -c copy \
-mpegts_original_network_id 0x1122 \
-mpegts_transport_stream_id 0x3344 \
-mpegts_service_id 0x5566 \
-mpegts_pmt_start_pid 0x1500 \
-mpegts_start_pid 0x150 \
-metadata service_provider="Some provider" \
-metadata service_name="Some Channel" \
-y out.ts
null
Null muxer.
This muxer does not generate any output file, it is mainly useful for
testing or benchmarking purposes.
For example to benchmark decoding with avconv you can use the command:
avconv-benchmark -i INPUT -f null out.null
Note that the above command does not read or write the out.null file,
but specifying the output file is required by the avconv syntax.
Alternatively you can write the command as:
avconv-benchmark -i INPUT -f null -
matroska
Matroska container muxer.
This muxer implements the matroska and webm container specs.
The recognized metadata settings in this muxer are:
title=title name
Name provided to a single track
language=language name
Specifies the language of the track in the Matroska languages form
STEREO_MODE=mode
Stereo 3D video layout of two views in a single video track
mono
video is not stereo
left_right
Both views are arranged side by side, Left-eye view is on the
left
bottom_top
Both views are arranged in top-bottom orientation, Left-eye
view is at bottom
top_bottom
Both views are arranged in top-bottom orientation, Left-eye
view is on top
checkerboard_rl
Each view is arranged in a checkerboard interleaved pattern,
Left-eye view being first
checkerboard_lr
Each view is arranged in a checkerboard interleaved pattern,
Right-eye view being first
row_interleaved_rl
Each view is constituted by a row based interleaving, Right-eye
view is first row
row_interleaved_lr
Each view is constituted by a row based interleaving, Left-eye
view is first row
col_interleaved_rl
Both views are arranged in a column based interleaving manner,
Right-eye view is first column
col_interleaved_lr
Both views are arranged in a column based interleaving manner,
Left-eye view is first column
anaglyph_cyan_red
All frames are in anaglyph format viewable through red-cyan
filters
right_left
Both views are arranged side by side, Right-eye view is on the
left
anaglyph_green_magenta
All frames are in anaglyph format viewable through green-
magenta filters
block_lr
Both eyes laced in one Block, Left-eye view is first
block_rl
Both eyes laced in one Block, Right-eye view is first
For example a 3D WebM clip can be created using the following command
line:
avconv-i sample_left_right_clip.mpg -an -c:v libvpx -metadata STEREO_MODE=left_right -y stereo_clip.webm
segment
Basic stream segmenter.
The segmenter muxer outputs streams to a number of separate files of
nearly fixed duration. Output filename pattern can be set in a fashion
similar to image2.
Every segment starts with a video keyframe, if a video stream is
present. The segment muxer works best with a single constant frame
rate video.
Optionally it can generate a flat list of the created segments, one
segment per line.
segment_format format
Override the inner container format, by default it is guessed by
the filename extension.
segment_time t
Set segment duration to t seconds.
segment_list name
Generate also a listfile named name.
segment_list_size size
Overwrite the listfile once it reaches size entries.
avconv-i in.mkv -c copy -map 0 -f segment -list out.list out%03d.nut
INPUT DEVICES
Input devices are configured elements in Libav which allow to access
the data coming from a multimedia device attached to your system.
When you configure your Libav build, all the supported input devices
are enabled by default. You can list all available ones using the
configure option "--list-indevs".
You can disable all the input devices using the configure option
"--disable-indevs", and selectively enable an input device using the
option "--enable-indev=INDEV", or you can disable a particular input
device using the option "--disable-indev=INDEV".
The option "-formats" of the av* tools will display the list of
supported input devices (amongst the demuxers).
A description of the currently available input devices follows.
alsa
ALSA (Advanced Linux Sound Architecture) input device.
To enable this input device during configuration you need libasound
installed on your system.
This device allows capturing from an ALSA device. The name of the
device to capture has to be an ALSA card identifier.
An ALSA identifier has the syntax:
hw:<CARD>[,<DEV>[,<SUBDEV>]]
where the DEV and SUBDEV components are optional.
The three arguments (in order: CARD,DEV,SUBDEV) specify card number or
identifier, device number and subdevice number (-1 means any).
To see the list of cards currently recognized by your system check the
files /proc/asound/cards and /proc/asound/devices.
For example to capture with avconv from an ALSA device with card id 0,
you may run the command:
avconv-f alsa -i hw:0 alsaout.wav
For more information see:
<http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html>
bktr
BSD video input device.
dv1394
Linux DV 1394 input device.
fbdev
Linux framebuffer input device.
The Linux framebuffer is a graphic hardware-independent abstraction
layer to show graphics on a computer monitor, typically on the console.
It is accessed through a file device node, usually /dev/fb0.
For more detailed information read the file
Documentation/fb/framebuffer.txt included in the Linux source tree.
To record from the framebuffer device /dev/fb0 with avconv:
avconv-f fbdev -r 10 -i /dev/fb0 out.avi
You can take a single screenshot image with the command:
avconv-f fbdev -frames:v 1 -r 1 -i /dev/fb0 screenshot.jpeg
See also <http://linux-fbdev.sourceforge.net/>, and fbset(1).
jack
JACK input device.
To enable this input device during configuration you need libjack
installed on your system.
A JACK input device creates one or more JACK writable clients, one for
each audio channel, with name client_name:input_N, where client_name is
the name provided by the application, and N is a number which
identifies the channel. Each writable client will send the acquired
data to the Libav input device.
Once you have created one or more JACK readable clients, you need to
connect them to one or more JACK writable clients.
To connect or disconnect JACK clients you can use the jack_connect and
jack_disconnect programs, or do it through a graphical interface, for
example with qjackctl.
To list the JACK clients and their properties you can invoke the
command jack_lsp.
Follows an example which shows how to capture a JACK readable client
with avconv.
# Create a JACK writable client with name "libav".
$ avconv-f jack -i libav -y out.wav
# Start the sample jack_metro readable client.
$ jack_metro -b 120 -d 0.2 -f 4000
# List the current JACK clients.
$ jack_lsp -c
system:capture_1
system:capture_2
system:playback_1
system:playback_2
libav:input_1
metro:120_bpm
# Connect metro to the avconv writable client.
$ jack_connect metro:120_bpm libav:input_1
For more information read: <http://jackaudio.org/>
libdc1394
IIDC1394 input device, based on libdc1394 and libraw1394.
oss
Open Sound System input device.
The filename to provide to the input device is the device node
representing the OSS input device, and is usually set to /dev/dsp.
For example to grab from /dev/dsp using avconv use the command:
avconv-f oss -i /dev/dsp /tmp/oss.wav
For more information about OSS see:
<http://manuals.opensound.com/usersguide/dsp.html>
pulse
pulseaudio input device.
To enable this input device during configuration you need libpulse-
simple installed in your system.
The filename to provide to the input device is a source device or the
string "default"
To list the pulse source devices and their properties you can invoke
the command pactl list sources.
avconv-f pulse -i default /tmp/pulse.wav
server AVOption
The syntax is:
-server <server name>
Connects to a specific server.
name AVOption
The syntax is:
-name <application name>
Specify the application name pulse will use when showing active
clients, by default it is "libav"
stream_name AVOption
The syntax is:
-stream_name <stream name>
Specify the stream name pulse will use when showing active streams, by
default it is "record"
sample_rate AVOption
The syntax is:
-sample_rate <samplerate>
Specify the samplerate in Hz, by default 48kHz is used.
channels AVOption
The syntax is:
-channels <N>
Specify the channels in use, by default 2 (stereo) is set.
frame_size AVOption
The syntax is:
-frame_size <bytes>
Specify the number of byte per frame, by default it is set to 1024.
fragment_size AVOption
The syntax is:
-fragment_size <bytes>
Specify the minimal buffering fragment in pulseaudio, it will affect
the audio latency. By default it is unset.
sndio
sndio input device.
To enable this input device during configuration you need libsndio
installed on your system.
The filename to provide to the input device is the device node
representing the sndio input device, and is usually set to /dev/audio0.
For example to grab from /dev/audio0 using avconv use the command:
avconv-f sndio -i /dev/audio0 /tmp/oss.wav
video4linux and video4linux2
Video4Linux and Video4Linux2 input video devices.
The name of the device to grab is a file device node, usually Linux
systems tend to automatically create such nodes when the device (e.g.
an USB webcam) is plugged into the system, and has a name of the kind
/dev/videoN, where N is a number associated to the device.
Video4Linux and Video4Linux2 devices only support a limited set of
widthxheight sizes and framerates. You can check which are supported
for example with the command dov4l for Video4Linux devices and using
-list_formats all for Video4Linux2 devices.
If the size for the device is set to 0x0, the input device will try to
autodetect the size to use. Only for the video4linux2 device, if the
frame rate is set to 0/0 the input device will use the frame rate value
already set in the driver.
Video4Linux support is deprecated since Linux 2.6.30, and will be
dropped in later versions.
Follow some usage examples of the video4linux devices with the av*
tools.
# Grab and show the input of a video4linux device, frame rate is set
# to the default of 25/1.
avplay -s 320x240 -f video4linux /dev/video0
# Grab and show the input of a video4linux2 device, autoadjust size.
avplay -f video4linux2 /dev/video0
# Grab and record the input of a video4linux2 device, autoadjust size,
# frame rate value defaults to 0/0 so it is read from the video4linux2
# driver.
avconv-f video4linux2 -i /dev/video0 out.mpeg
vfwcap
VfW (Video for Windows) capture input device.
The filename passed as input is the capture driver number, ranging from
0 to 9. You may use "list" as filename to print a list of drivers. Any
other filename will be interpreted as device number 0.
x11grab
X11 video input device.
This device allows to capture a region of an X11 display.
The filename passed as input has the syntax:
[<hostname>]:<display_number>.<screen_number>[+<x_offset>,<y_offset>]
hostname:display_number.screen_number specifies the X11 display name of
the screen to grab from. hostname can be ommitted, and defaults to
"localhost". The environment variable DISPLAY contains the default
display name.
x_offset and y_offset specify the offsets of the grabbed area with
respect to the top-left border of the X11 screen. They default to 0.
Check the X11 documentation (e.g. man X) for more detailed information.
Use the dpyinfo program for getting basic information about the
properties of your X11 display (e.g. grep for "name" or "dimensions").
For example to grab from :0.0 using avconv:
avconv-f x11grab -r 25 -s cif -i :0.0 out.mpg
# Grab at position 10,20.
avconv-f x11grab -r 25 -s cif -i :0.0+10,20 out.mpg
follow_mouse AVOption
The syntax is:
-follow_mouse centered|<PIXELS>
When it is specified with "centered", the grabbing region follows the
mouse pointer and keeps the pointer at the center of region; otherwise,
the region follows only when the mouse pointer reaches within PIXELS
(greater than zero) to the edge of region.
For example:
avconv-f x11grab -follow_mouse centered -r 25 -s cif -i :0.0 out.mpg
# Follows only when the mouse pointer reaches within 100 pixels to edge
avconv-f x11grab -follow_mouse 100 -r 25 -s cif -i :0.0 out.mpg
show_region AVOption
The syntax is:
-show_region 1
If show_region AVOption is specified with 1, then the grabbing region
will be indicated on screen. With this option, it's easy to know what
is being grabbed if only a portion of the screen is grabbed.
For example:
avconv-f x11grab -show_region 1 -r 25 -s cif -i :0.0+10,20 out.mpg
# With follow_mouse
avconv-f x11grab -follow_mouse centered -show_region 1 -r 25 -s cif -i :0.0 out.mpg
OUTPUT DEVICES
Output devices are configured elements in Libav which allow to write
multimedia data to an output device attached to your system.
When you configure your Libav build, all the supported output devices
are enabled by default. You can list all available ones using the
configure option "--list-outdevs".
You can disable all the output devices using the configure option
"--disable-outdevs", and selectively enable an output device using the
option "--enable-outdev=OUTDEV", or you can disable a particular input
device using the option "--disable-outdev=OUTDEV".
The option "-formats" of the av* tools will display the list of enabled
output devices (amongst the muxers).
A description of the currently available output devices follows.
alsa
ALSA (Advanced Linux Sound Architecture) output device.
oss
OSS (Open Sound System) output device.
sndio
sndio audio output device.
PROTOCOLS
Protocols are configured elements in Libav which allow to access
resources which require the use of a particular protocol.
When you configure your Libav build, all the supported protocols are
enabled by default. You can list all available ones using the configure
option "--list-protocols".
You can disable all the protocols using the configure option
"--disable-protocols", and selectively enable a protocol using the
option "--enable-protocol=PROTOCOL", or you can disable a particular
protocol using the option "--disable-protocol=PROTOCOL".
The option "-protocols" of the av* tools will display the list of
supported protocols.
A description of the currently available protocols follows.
applehttp
Read Apple HTTP Live Streaming compliant segmented stream as a uniform
one. The M3U8 playlists describing the segments can be remote HTTP
resources or local files, accessed using the standard file protocol.
HTTP is default, specific protocol can be declared by specifying
"+proto" after the applehttp URI scheme name, where proto is either
"file" or "http".
applehttp://host/path/to/remote/resource.m3u8
applehttp+http://host/path/to/remote/resource.m3u8
applehttp+file://path/to/local/resource.m3u8
concat
Physical concatenation protocol.
Allow to read and seek from many resource in sequence as if they were a
unique resource.
A URL accepted by this protocol has the syntax:
concat:<URL1>|<URL2>|...|<URLN>
where URL1, URL2, ..., URLN are the urls of the resource to be
concatenated, each one possibly specifying a distinct protocol.
For example to read a sequence of files split1.mpeg, split2.mpeg,
split3.mpeg with avplay use the command:
avplay concat:split1.mpeg\|split2.mpeg\|split3.mpeg
Note that you may need to escape the character "|" which is special for
many shells.
file
File access protocol.
Allow to read from or read to a file.
For example to read from a file input.mpeg with avconv use the command:
avconv-i file:input.mpeg output.mpeg
The av* tools default to the file protocol, that is a resource
specified with the name "FILE.mpeg" is interpreted as the URL
"file:FILE.mpeg".
gopher
Gopher protocol.
http
HTTP (Hyper Text Transfer Protocol).
mmst
MMS (Microsoft Media Server) protocol over TCP.
mmsh
MMS (Microsoft Media Server) protocol over HTTP.
The required syntax is:
mmsh://<server>[:<port>][/<app>][/<playpath>]
md5
MD5 output protocol.
Computes the MD5 hash of the data to be written, and on close writes
this to the designated output or stdout if none is specified. It can be
used to test muxers without writing an actual file.
Some examples follow.
# Write the MD5 hash of the encoded AVI file to the file output.avi.md5.
avconv-i input.flv -f avi -y md5:output.avi.md5
# Write the MD5 hash of the encoded AVI file to stdout.
avconv-i input.flv -f avi -y md5:
Note that some formats (typically MOV) require the output protocol to
be seekable, so they will fail with the MD5 output protocol.
pipe
UNIX pipe access protocol.
Allow to read and write from UNIX pipes.
The accepted syntax is:
pipe:[<number>]
number is the number corresponding to the file descriptor of the pipe
(e.g. 0 for stdin, 1 for stdout, 2 for stderr). If number is not
specified, by default the stdout file descriptor will be used for
writing, stdin for reading.
For example to read from stdin with avconv:
cat test.wav | avconv-i pipe:0
# ...this is the same as...
cat test.wav | avconv-i pipe:
For writing to stdout with avconv:
avconv-i test.wav -f avi pipe:1 | cat > test.avi
# ...this is the same as...
avconv-i test.wav -f avi pipe: | cat > test.avi
Note that some formats (typically MOV), require the output protocol to
be seekable, so they will fail with the pipe output protocol.
rtmp
Real-Time Messaging Protocol.
The Real-Time Messaging Protocol (RTMP) is used for streaming
multimedia content across a TCP/IP network.
The required syntax is:
rtmp://<server>[:<port>][/<app>][/<playpath>]
The accepted parameters are:
server
The address of the RTMP server.
port
The number of the TCP port to use (by default is 1935).
app It is the name of the application to access. It usually corresponds
to the path where the application is installed on the RTMP server
(e.g. /ondemand/, /flash/live/, etc.).
playpath
It is the path or name of the resource to play with reference to
the application specified in app, may be prefixed by "mp4:".
For example to read with avplay a multimedia resource named "sample"
from the application "vod" from an RTMP server "myserver":
avplay rtmp://myserver/vod/sample
rtmp, rtmpe, rtmps, rtmpt, rtmpte
Real-Time Messaging Protocol and its variants supported through
librtmp.
Requires the presence of the librtmp headers and library during
configuration. You need to explicitly configure the build with
"--enable-librtmp". If enabled this will replace the native RTMP
protocol.
This protocol provides most client functions and a few server functions
needed to support RTMP, RTMP tunneled in HTTP (RTMPT), encrypted RTMP
(RTMPE), RTMP over SSL/TLS (RTMPS) and tunneled variants of these
encrypted types (RTMPTE, RTMPTS).
The required syntax is:
<rtmp_proto>://<server>[:<port>][/<app>][/<playpath>] <options>
where rtmp_proto is one of the strings "rtmp", "rtmpt", "rtmpe",
"rtmps", "rtmpte", "rtmpts" corresponding to each RTMP variant, and
server, port, app and playpath have the same meaning as specified for
the RTMP native protocol. options contains a list of space-separated
options of the form key=val.
See the librtmp manual page (man 3 librtmp) for more information.
For example, to stream a file in real-time to an RTMP server using
avconv:
avconv-re -i myfile -f flv rtmp://myserver/live/mystream
To play the same stream using avplay:
avplay "rtmp://myserver/live/mystream live=1"
rtp
Real-Time Protocol.
rtsp
RTSP is not technically a protocol handler in libavformat, it is a
demuxer and muxer. The demuxer supports both normal RTSP (with data
transferred over RTP; this is used by e.g. Apple and Microsoft) and
Real-RTSP (with data transferred over RDT).
The muxer can be used to send a stream using RTSP ANNOUNCE to a server
supporting it (currently Darwin Streaming Server and Mischa
Spiegelmock's
RTSP server ("http://github.com/revmischa/rtsp-server")).
The required syntax for a RTSP url is:
rtsp://<hostname>[:<port>]/<path>
The following options (set on the avconv/avplay command line, or set in
code via "AVOption"s or in "avformat_open_input"), are supported:
Flags for "rtsp_transport":
udp Use UDP as lower transport protocol.
tcp Use TCP (interleaving within the RTSP control channel) as lower
transport protocol.
udp_multicast
Use UDP multicast as lower transport protocol.
http
Use HTTP tunneling as lower transport protocol, which is useful for
passing proxies.
Multiple lower transport protocols may be specified, in that case they
are tried one at a time (if the setup of one fails, the next one is
tried). For the muxer, only the "tcp" and "udp" options are supported.
Flags for "rtsp_flags":
filter_src
Accept packets only from negotiated peer address and port.
When receiving data over UDP, the demuxer tries to reorder received
packets (since they may arrive out of order, or packets may get lost
totally). In order for this to be enabled, a maximum delay must be
specified in the "max_delay" field of AVFormatContext.
When watching multi-bitrate Real-RTSP streams with avplay, the streams
to display can be chosen with "-vst" n and "-ast" n for video and audio
respectively, and can be switched on the fly by pressing "v" and "a".
Example command lines:
To watch a stream over UDP, with a max reordering delay of 0.5 seconds:
avplay -max_delay 500000 -rtsp_transport udp rtsp://server/video.mp4
To watch a stream tunneled over HTTP:
avplay -rtsp_transport http rtsp://server/video.mp4
To send a stream in realtime to a RTSP server, for others to watch:
avconv-re -i <input> -f rtsp -muxdelay 0.1 rtsp://server/live.sdp
sap
Session Announcement Protocol (RFC 2974). This is not technically a
protocol handler in libavformat, it is a muxer and demuxer. It is used
for signalling of RTP streams, by announcing the SDP for the streams
regularly on a separate port.
Muxer
The syntax for a SAP url given to the muxer is:
sap://<destination>[:<port>][?<options>]
The RTP packets are sent to destination on port port, or to port 5004
if no port is specified. options is a "&"-separated list. The
following options are supported:
announce_addr=address
Specify the destination IP address for sending the announcements
to. If omitted, the announcements are sent to the commonly used
SAP announcement multicast address 224.2.127.254 (sap.mcast.net),
or ff0e::2:7ffe if destination is an IPv6 address.
announce_port=port
Specify the port to send the announcements on, defaults to 9875 if
not specified.
ttl=ttl
Specify the time to live value for the announcements and RTP
packets, defaults to 255.
same_port=0|1
If set to 1, send all RTP streams on the same port pair. If zero
(the default), all streams are sent on unique ports, with each
stream on a port 2 numbers higher than the previous. VLC/Live555
requires this to be set to 1, to be able to receive the stream.
The RTP stack in libavformat for receiving requires all streams to
be sent on unique ports.
Example command lines follow.
To broadcast a stream on the local subnet, for watching in VLC:
avconv-re -i <input> -f sap sap://224.0.0.255?same_port=1
Similarly, for watching in avplay:
avconv-re -i <input> -f sap sap://224.0.0.255
And for watching in avplay, over IPv6:
avconv-re -i <input> -f sap sap://[ff0e::1:2:3:4]
Demuxer
The syntax for a SAP url given to the demuxer is:
sap://[<address>][:<port>]
address is the multicast address to listen for announcements on, if
omitted, the default 224.2.127.254 (sap.mcast.net) is used. port is the
port that is listened on, 9875 if omitted.
The demuxers listens for announcements on the given address and port.
Once an announcement is received, it tries to receive that particular
stream.
Example command lines follow.
To play back the first stream announced on the normal SAP multicast
address:
avplay sap://
To play back the first stream announced on one the default IPv6 SAP
multicast address:
avplay sap://[ff0e::2:7ffe]
tcp
Trasmission Control Protocol.
The required syntax for a TCP url is:
tcp://<hostname>:<port>[?<options>]
listen
Listen for an incoming connection
avconv-i <input> -f <format> tcp://<hostname>:<port>?listen
avplay tcp://<hostname>:<port>
udp
User Datagram Protocol.
The required syntax for a UDP url is:
udp://<hostname>:<port>[?<options>]
options contains a list of &-seperated options of the form key=val.
Follow the list of supported options.
buffer_size=size
set the UDP buffer size in bytes
localport=port
override the local UDP port to bind with
localaddr=addr
Choose the local IP address. This is useful e.g. if sending
multicast and the host has multiple interfaces, where the user can
choose which interface to send on by specifying the IP address of
that interface.
pkt_size=size
set the size in bytes of UDP packets
reuse=1|0
explicitly allow or disallow reusing UDP sockets
ttl=ttl
set the time to live value (for multicast only)
connect=1|0
Initialize the UDP socket with "connect()". In this case, the
destination address can't be changed with ff_udp_set_remote_url
later. If the destination address isn't known at the start, this
option can be specified in ff_udp_set_remote_url, too. This allows
finding out the source address for the packets with getsockname,
and makes writes return with AVERROR(ECONNREFUSED) if "destination
unreachable" is received. For receiving, this gives the benefit of
only receiving packets from the specified peer address/port.
Some usage examples of the udp protocol with avconv follow.
To stream over UDP to a remote endpoint:
avconv-i <input> -f <format> udp://<hostname>:<port>
To stream in mpegts format over UDP using 188 sized UDP packets, using
a large input buffer:
avconv-i <input> -f mpegts udp://<hostname>:<port>?pkt_size=188&buffer_size=65535
To receive over UDP from a remote endpoint:
avconv-i udp://[<multicast-address>]:<port>
BITSTREAM FILTERS
When you configure your Libav build, all the supported bitstream
filters are enabled by default. You can list all available ones using
the configure option "--list-bsfs".
You can disable all the bitstream filters using the configure option
"--disable-bsfs", and selectively enable any bitstream filter using the
option "--enable-bsf=BSF", or you can disable a particular bitstream
filter using the option "--disable-bsf=BSF".
The option "-bsfs" of the av* tools will display the list of all the
supported bitstream filters included in your build.
Below is a description of the currently available bitstream filters.
aac_adtstoasc
chomp
dump_extradata
h264_mp4toannexb
imx_dump_header
mjpeg2jpeg
Convert MJPEG/AVI1 packets to full JPEG/JFIF packets.
MJPEG is a video codec wherein each video frame is essentially a JPEG
image. The individual frames can be extracted without loss, e.g. by
avconv-i ../some_mjpeg.avi -c:v copy frames_%d.jpg
Unfortunately, these chunks are incomplete JPEG images, because they
lack the DHT segment required for decoding. Quoting from
<http://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml>:
Avery Lee, writing in the rec.video.desktop newsgroup in 2001,
commented that "MJPEG, or at least the MJPEG in AVIs having the MJPG
fourcc, is restricted JPEG with a fixed -- and *omitted* -- Huffman
table. The JPEG must be YCbCr colorspace, it must be 4:2:2, and it must
use basic Huffman encoding, not arithmetic or progressive. . . . You
can indeed extract the MJPEG frames and decode them with a regular JPEG
decoder, but you have to prepend the DHT segment to them, or else the
decoder won't have any idea how to decompress the data. The exact table
necessary is given in the OpenDML spec."
This bitstream filter patches the header of frames extracted from an
MJPEG stream (carrying the AVI1 header ID and lacking a DHT segment) to
produce fully qualified JPEG images.
avconv-i mjpeg-movie.avi -c:v copy -vbsf mjpeg2jpeg frame_%d.jpg
exiftran -i -9 frame*.jpg
avconv-i frame_%d.jpg -c:v copy rotated.avi
mjpega_dump_header
movsub
mp3_header_compress
mp3_header_decompress
noise
remove_extradata
FILTERGRAPH DESCRIPTION
A filtergraph is a directed graph of connected filters. It can contain
cycles, and there can be multiple links between a pair of filters. Each
link has one input pad on one side connecting it to one filter from
which it takes its input, and one output pad on the other side
connecting it to the one filter accepting its output.
Each filter in a filtergraph is an instance of a filter class
registered in the application, which defines the features and the
number of input and output pads of the filter.
A filter with no input pads is called a "source", a filter with no
output pads is called a "sink".
Filtergraph syntax
A filtergraph can be represented using a textual representation, which
is recognized by the "-vf" and "-af" options in avconv and avplay, and
by the "av_parse_graph()" function defined in
libavfilter/avfiltergraph.
A filterchain consists of a sequence of connected filters, each one
connected to the previous one in the sequence. A filterchain is
represented by a list of ","-separated filter descriptions.
A filtergraph consists of a sequence of filterchains. A sequence of
filterchains is represented by a list of ";"-separated filterchain
descriptions.
A filter is represented by a string of the form:
[in_link_1]...[in_link_N]filter_name=arguments[out_link_1]...[out_link_M]
filter_name is the name of the filter class of which the described
filter is an instance of, and has to be the name of one of the filter
classes registered in the program. The name of the filter class is
optionally followed by a string "=arguments".
arguments is a string which contains the parameters used to initialize
the filter instance, and are described in the filter descriptions
below.
The list of arguments can be quoted using the character "'" as initial
and ending mark, and the character '\' for escaping the characters
within the quoted text; otherwise the argument string is considered
terminated when the next special character (belonging to the set
"[]=;,") is encountered.
The name and arguments of the filter are optionally preceded and
followed by a list of link labels. A link label allows to name a link
and associate it to a filter output or input pad. The preceding labels
in_link_1 ... in_link_N, are associated to the filter input pads, the
following labels out_link_1 ... out_link_M, are associated to the
output pads.
When two link labels with the same name are found in the filtergraph, a
link between the corresponding input and output pad is created.
If an output pad is not labelled, it is linked by default to the first
unlabelled input pad of the next filter in the filterchain. For
example in the filterchain:
nullsrc, split[L1], [L2]overlay, nullsink
the split filter instance has two output pads, and the overlay filter
instance two input pads. The first output pad of split is labelled
"L1", the first input pad of overlay is labelled "L2", and the second
output pad of split is linked to the second input pad of overlay, which
are both unlabelled.
In a complete filterchain all the unlabelled filter input and output
pads must be connected. A filtergraph is considered valid if all the
filter input and output pads of all the filterchains are connected.
Follows a BNF description for the filtergraph syntax:
<NAME> ::= sequence of alphanumeric characters and '_'
<LINKLABEL> ::= "[" <NAME> "]"
<LINKLABELS> ::= <LINKLABEL> [<LINKLABELS>]
<FILTER_ARGUMENTS> ::= sequence of chars (eventually quoted)
<FILTER> ::= [<LINKLABELS>] <NAME> ["=" <FILTER_ARGUMENTS>] [<LINKLABELS>]
<FILTERCHAIN> ::= <FILTER> [,<FILTERCHAIN>]
<FILTERGRAPH> ::= <FILTERCHAIN> [;<FILTERGRAPH>]
AUDIO FILTERS
When you configure your Libav build, you can disable any of the
existing filters using --disable-filters. The configure output will
show the audio filters included in your build.
Below is a description of the currently available audio filters.
anull
Pass the audio source unchanged to the output.
AUDIO SOURCES
Below is a description of the currently available audio sources.
anullsrc
Null audio source, never return audio frames. It is mainly useful as a
template and to be employed in analysis / debugging tools.
It accepts as optional parameter a string of the form
sample_rate:channel_layout.
sample_rate specify the sample rate, and defaults to 44100.
channel_layout specify the channel layout, and can be either an integer
or a string representing a channel layout. The default value of
channel_layout is 3, which corresponds to CH_LAYOUT_STEREO.
Check the channel_layout_map definition in libavcodec/audioconvert.c
for the mapping between strings and channel layout values.
Follow some examples:
# set the sample rate to 48000 Hz and the channel layout to CH_LAYOUT_MONO.
anullsrc=48000:4
# same as
anullsrc=48000:mono
AUDIO SINKS
Below is a description of the currently available audio sinks.
anullsink
Null audio sink, do absolutely nothing with the input audio. It is
mainly useful as a template and to be employed in analysis / debugging
tools.
VIDEO FILTERS
When you configure your Libav build, you can disable any of the
existing filters using --disable-filters. The configure output will
show the video filters included in your build.
Below is a description of the currently available video filters.
blackframe
Detect frames that are (almost) completely black. Can be useful to
detect chapter transitions or commercials. Output lines consist of the
frame number of the detected frame, the percentage of blackness, the
position in the file if known or -1 and the timestamp in seconds.
In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.
The filter accepts the syntax:
blackframe[=<amount>:[<threshold>]]
amount is the percentage of the pixels that have to be below the
threshold, and defaults to 98.
threshold is the threshold below which a pixel value is considered
black, and defaults to 32.
boxblur
Apply boxblur algorithm to the input video.
This filter accepts the parameters:
luma_power:luma_radius:chroma_radius:chroma_power:alpha_radius:alpha_power
Chroma and alpha parameters are optional, if not specified they default
to the corresponding values set for luma_radius and luma_power.
luma_radius, chroma_radius, and alpha_radius represent the radius in
pixels of the box used for blurring the corresponding input plane. They
are expressions, and can contain the following constants:
w, h
the input width and height in pixels
cw, ch
the input chroma image width and height in pixels
hsub, vsub
horizontal and vertical chroma subsample values. For example for
the pixel format "yuv422p" hsub is 2 and vsub is 1.
The radius must be a non-negative number, and must not be greater than
the value of the expression "min(w,h)/2" for the luma and alpha planes,
and of "min(cw,ch)/2" for the chroma planes.
luma_power, chroma_power, and alpha_power represent how many times the
boxblur filter is applied to the corresponding plane.
Some examples follow:
· Apply a boxblur filter with luma, chroma, and alpha radius set to
2:
boxblur=2:1
· Set luma radius to 2, alpha and chroma radius to 0
boxblur=2:1:0:0:0:0
· Set luma and chroma radius to a fraction of the video dimension
boxblur=min(h,w)/10:1:min(cw,ch)/10:1
copy
Copy the input source unchanged to the output. Mainly useful for
testing purposes.
crop
Crop the input video to out_w:out_h:x:y.
The parameters are expressions containing the following constants:
E, PI, PHI
the corresponding mathematical approximated values for e (euler
number), pi (greek PI), PHI (golden ratio)
x, y
the computed values for x and y. They are evaluated for each new
frame.
in_w, in_h
the input width and height
iw, ih
same as in_w and in_h
out_w, out_h
the output (cropped) width and height
ow, oh
same as out_w and out_h
n the number of input frame, starting from 0
pos the position in the file of the input frame, NAN if unknown
t timestamp expressed in seconds, NAN if the input timestamp is
unknown
The out_w and out_h parameters specify the expressions for the width
and height of the output (cropped) video. They are evaluated just at
the configuration of the filter.
The default value of out_w is "in_w", and the default value of out_h is
"in_h".
The expression for out_w may depend on the value of out_h, and the
expression for out_h may depend on out_w, but they cannot depend on x
and y, as x and y are evaluated after out_w and out_h.
The x and y parameters specify the expressions for the position of the
top-left corner of the output (non-cropped) area. They are evaluated
for each frame. If the evaluated value is not valid, it is approximated
to the nearest valid value.
The default value of x is "(in_w-out_w)/2", and the default value for y
is "(in_h-out_h)/2", which set the cropped area at the center of the
input image.
The expression for x may depend on y, and the expression for y may
depend on x.
Follow some examples:
# crop the central input area with size 100x100
crop=100:100
# crop the central input area with size 2/3 of the input video
"crop=2/3*in_w:2/3*in_h"
# crop the input video central square
crop=in_h
# delimit the rectangle with the top-left corner placed at position
# 100:100 and the right-bottom corner corresponding to the right-bottom
# corner of the input image.
crop=in_w-100:in_h-100:100:100
# crop 10 pixels from the left and right borders, and 20 pixels from
# the top and bottom borders
"crop=in_w-2*10:in_h-2*20"
# keep only the bottom right quarter of the input image
"crop=in_w/2:in_h/2:in_w/2:in_h/2"
# crop height for getting Greek harmony
"crop=in_w:1/PHI*in_w"
# trembling effect
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(n/7)"
# erratic camera effect depending on timestamp
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(t*10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(t*13)"
# set x depending on the value of y
"crop=in_w/2:in_h/2:y:10+10*sin(n/10)"
cropdetect
Auto-detect crop size.
Calculate necessary cropping parameters and prints the recommended
parameters through the logging system. The detected dimensions
correspond to the non-black area of the input video.
It accepts the syntax:
cropdetect[=<limit>[:<round>[:<reset>]]]
limit
Threshold, which can be optionally specified from nothing (0) to
everything (255), defaults to 24.
round
Value which the width/height should be divisible by, defaults to
16. The offset is automatically adjusted to center the video. Use 2
to get only even dimensions (needed for 4:2:2 video). 16 is best
when encoding to most video codecs.
reset
Counter that determines after how many frames cropdetect will reset
the previously detected largest video area and start over to detect
the current optimal crop area. Defaults to 0.
This can be useful when channel logos distort the video area. 0
indicates never reset and return the largest area encountered
during playback.
delogo
Suppress a TV station logo by a simple interpolation of the surrounding
pixels. Just set a rectangle covering the logo and watch it disappear
(and sometimes something even uglier appear - your mileage may vary).
The filter accepts parameters as a string of the form "x:y:w:h:band",
or as a list of key=value pairs, separated by ":".
The description of the accepted parameters follows.
x, y
Specify the top left corner coordinates of the logo. They must be
specified.
w, h
Specify the width and height of the logo to clear. They must be
specified.
band, t
Specify the thickness of the fuzzy edge of the rectangle (added to
w and h). The default value is 4.
show
When set to 1, a green rectangle is drawn on the screen to simplify
finding the right x, y, w, h parameters, and band is set to 4. The
default value is 0.
Some examples follow.
· Set a rectangle covering the area with top left corner coordinates
0,0 and size 100x77, setting a band of size 10:
delogo=0:0:100:77:10
· As the previous example, but use named options:
delogo=x=0:y=0:w=100:h=77:band=10
drawbox
Draw a colored box on the input image.
It accepts the syntax:
drawbox=<x>:<y>:<width>:<height>:<color>
x, y
Specify the top left corner coordinates of the box. Default to 0.
width, height
Specify the width and height of the box, if 0 they are interpreted
as the input width and height. Default to 0.
color
Specify the color of the box to write, it can be the name of a
color (case insensitive match) or a 0xRRGGBB[AA] sequence.
Follow some examples:
# draw a black box around the edge of the input image
drawbox
# draw a box with color red and an opacity of 50%
drawbox=10:20:200:60:red@0.5"
drawtext
Draw text string or text from specified file on top of video using the
libfreetype library.
To enable compilation of this filter you need to configure Libav with
"--enable-libfreetype".
The filter also recognizes strftime() sequences in the provided text
and expands them accordingly. Check the documentation of strftime().
The filter accepts parameters as a list of key=value pairs, separated
by ":".
The description of the accepted parameters follows.
fontfile
The font file to be used for drawing text. Path must be included.
This parameter is mandatory.
text
The text string to be drawn. The text must be a sequence of UTF-8
encoded characters. This parameter is mandatory if no file is
specified with the parameter textfile.
textfile
A text file containing text to be drawn. The text must be a
sequence of UTF-8 encoded characters.
This parameter is mandatory if no text string is specified with the
parameter text.
If both text and textfile are specified, an error is thrown.
x, y
The offsets where text will be drawn within the video frame.
Relative to the top/left border of the output image. They accept
expressions similar to the overlay filter:
x, y
the computed values for x and y. They are evaluated for each
new frame.
main_w, main_h
main input width and height
W, H
same as main_w and main_h
text_w, text_h
rendered text width and height
w, h
same as text_w and text_h
n the number of frames processed, starting from 0
t timestamp expressed in seconds, NAN if the input timestamp is
unknown
The default value of x and y is 0.
fontsize
The font size to be used for drawing text. The default value of
fontsize is 16.
fontcolor
The color to be used for drawing fonts. Either a string (e.g.
"red") or in 0xRRGGBB[AA] format (e.g. "0xff000033"), possibly
followed by an alpha specifier. The default value of fontcolor is
"black".
boxcolor
The color to be used for drawing box around text. Either a string
(e.g. "yellow") or in 0xRRGGBB[AA] format (e.g. "0xff00ff"),
possibly followed by an alpha specifier. The default value of
boxcolor is "white".
box Used to draw a box around text using background color. Value
should be either 1 (enable) or 0 (disable). The default value of
box is 0.
shadowx, shadowy
The x and y offsets for the text shadow position with respect to
the position of the text. They can be either positive or negative
values. Default value for both is "0".
shadowcolor
The color to be used for drawing a shadow behind the drawn text.
It can be a color name (e.g. "yellow") or a string in the
0xRRGGBB[AA] form (e.g. "0xff00ff"), possibly followed by an alpha
specifier. The default value of shadowcolor is "black".
ft_load_flags
Flags to be used for loading the fonts.
The flags map the corresponding flags supported by libfreetype, and
are a combination of the following values:
default
no_scale
no_hinting
render
no_bitmap
vertical_layout
force_autohint
crop_bitmap
pedantic
ignore_global_advance_width
no_recurse
ignore_transform
monochrome
linear_design
no_autohint
end table
Default value is "render".
For more information consult the documentation for the FT_LOAD_*
libfreetype flags.
tabsize
The size in number of spaces to use for rendering the tab. Default
value is 4.
For example the command:
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'"
will draw "Test Text" with font FreeSerif, using the default values for
the optional parameters.
The command:
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text':\
x=100: y=50: fontsize=24: fontcolor=yellow@0.2: box=1: boxcolor=red@0.2"
will draw 'Test Text' with font FreeSerif of size 24 at position x=100
and y=50 (counting from the top-left corner of the screen), text is
yellow with a red box around it. Both the text and the box have an
opacity of 20%.
Note that the double quotes are not necessary if spaces are not used
within the parameter list.
For more information about libfreetype, check:
<http://www.freetype.org/>.
fade
Apply fade-in/out effect to input video.
It accepts the parameters: type:start_frame:nb_frames
type specifies if the effect type, can be either "in" for fade-in, or
"out" for a fade-out effect.
start_frame specifies the number of the start frame for starting to
apply the fade effect.
nb_frames specifies the number of frames for which the fade effect has
to last. At the end of the fade-in effect the output video will have
the same intensity as the input video, at the end of the fade-out
transition the output video will be completely black.
A few usage examples follow, usable too as test scenarios.
# fade in first 30 frames of video
fade=in:0:30
# fade out last 45 frames of a 200-frame video
fade=out:155:45
# fade in first 25 frames and fade out last 25 frames of a 1000-frame video
fade=in:0:25, fade=out:975:25
# make first 5 frames black, then fade in from frame 5-24
fade=in:5:20
fieldorder
Transform the field order of the input video.
It accepts one parameter which specifies the required field order that
the input interlaced video will be transformed to. The parameter can
assume one of the following values:
0 or bff
output bottom field first
1 or tff
output top field first
Default value is "tff".
Transformation is achieved by shifting the picture content up or down
by one line, and filling the remaining line with appropriate picture
content. This method is consistent with most broadcast field order
converters.
If the input video is not flagged as being interlaced, or it is already
flagged as being of the required output field order then this filter
does not alter the incoming video.
This filter is very useful when converting to or from PAL DV material,
which is bottom field first.
For example:
./avconv -i in.vob -vf "fieldorder=bff" out.dv
fifo
Buffer input images and send them when they are requested.
This filter is mainly useful when auto-inserted by the libavfilter
framework.
The filter does not take parameters.
format
Convert the input video to one of the specified pixel formats.
Libavfilter will try to pick one that is supported for the input to the
next filter.
The filter accepts a list of pixel format names, separated by ":", for
example "yuv420p:monow:rgb24".
Some examples follow:
# convert the input video to the format "yuv420p"
format=yuv420p
# convert the input video to any of the formats in the list
format=yuv420p:yuv444p:yuv410p
frei0r
Apply a frei0r effect to the input video.
To enable compilation of this filter you need to install the frei0r
header and configure Libav with --enable-frei0r.
The filter supports the syntax:
<filter_name>[{:|=}<param1>:<param2>:...:<paramN>]
filter_name is the name to the frei0r effect to load. If the
environment variable FREI0R_PATH is defined, the frei0r effect is
searched in each one of the directories specified by the colon
separated list in FREIOR_PATH, otherwise in the standard frei0r paths,
which are in this order: HOME/.frei0r-1/lib/, /usr/local/lib/frei0r-1/,
/usr/lib/frei0r-1/.
param1, param2, ... , paramN specify the parameters for the frei0r
effect.
A frei0r effect parameter can be a boolean (whose values are specified
with "y" and "n"), a double, a color (specified by the syntax R/G/B, R,
G, and B being float numbers from 0.0 to 1.0) or by an
"av_parse_color()" color description), a position (specified by the
syntax X/Y, X and Y being float numbers) and a string.
The number and kind of parameters depend on the loaded effect. If an
effect parameter is not specified the default value is set.
Some examples follow:
# apply the distort0r effect, set the first two double parameters
frei0r=distort0r:0.5:0.01
# apply the colordistance effect, takes a color as first parameter
frei0r=colordistance:0.2/0.3/0.4
frei0r=colordistance:violet
frei0r=colordistance:0x112233
# apply the perspective effect, specify the top left and top right
# image positions
frei0r=perspective:0.2/0.2:0.8/0.2
For more information see: <http://piksel.org/frei0r>
gradfun
Fix the banding artifacts that are sometimes introduced into nearly
flat regions by truncation to 8bit colordepth. Interpolate the
gradients that should go where the bands are, and dither them.
This filter is designed for playback only. Do not use it prior to
lossy compression, because compression tends to lose the dither and
bring back the bands.
The filter takes two optional parameters, separated by ':':
strength:radius
strength is the maximum amount by which the filter will change any one
pixel. Also the threshold for detecting nearly flat regions. Acceptable
values range from .51 to 255, default value is 1.2, out-of-range values
will be clipped to the valid range.
radius is the neighborhood to fit the gradient to. A larger radius
makes for smoother gradients, but also prevents the filter from
modifying the pixels near detailed regions. Acceptable values are 8-32,
default value is 16, out-of-range values will be clipped to the valid
range.
# default parameters
gradfun=1.2:16
# omitting radius
gradfun=1.2
hflip
Flip the input video horizontally.
For example to horizontally flip the input video with avconv:
avconv-i in.avi -vf "hflip" out.avi
hqdn3d
High precision/quality 3d denoise filter. This filter aims to reduce
image noise producing smooth images and making still images really
still. It should enhance compressibility.
It accepts the following optional parameters:
luma_spatial:chroma_spatial:luma_tmp:chroma_tmp
luma_spatial
a non-negative float number which specifies spatial luma strength,
defaults to 4.0
chroma_spatial
a non-negative float number which specifies spatial chroma
strength, defaults to 3.0*luma_spatial/4.0
luma_tmp
a float number which specifies luma temporal strength, defaults to
6.0*luma_spatial/4.0
chroma_tmp
a float number which specifies chroma temporal strength, defaults
to luma_tmp*chroma_spatial/luma_spatial
lut, lutrgb, lutyuv
Compute a look-up table for binding each pixel component input value to
an output value, and apply it to input video.
lutyuv applies a lookup table to a YUV input video, lutrgb to an RGB
input video.
These filters accept in input a ":"-separated list of options, which
specify the expressions used for computing the lookup table for the
corresponding pixel component values.
The lut filter requires either YUV or RGB pixel formats in input, and
accepts the options:
c0 (first pixel component) c1 (second pixel component) c2 (third
pixel component) c3 (fourth pixel component, corresponds to the
alpha component)
The exact component associated to each option depends on the format in
input.
The lutrgb filter requires RGB pixel formats in input, and accepts the
options:
r (red component) g (green component) b (blue component) a (alpha
component)
The lutyuv filter requires YUV pixel formats in input, and accepts the
options:
y (Y/luminance component) u (U/Cb component) v (V/Cr component) a
(alpha component)
The expressions can contain the following constants and functions:
E, PI, PHI
the corresponding mathematical approximated values for e (euler
number), pi (greek PI), PHI (golden ratio)
w, h
the input width and height
val input value for the pixel component
clipval
the input value clipped in the minval-maxval range
maxval
maximum value for the pixel component
minval
minimum value for the pixel component
negval
the negated value for the pixel component value clipped in the
minval-maxval range , it corresponds to the expression
"maxval-clipval+minval"
clip(val)
the computed value in val clipped in the minval-maxval range
gammaval(gamma)
the computed gamma correction value of the pixel component value
clipped in the minval-maxval range, corresponds to the expression
"pow((clipval-minval)/(maxval-minval),gamma)*(maxval-minval)+minval"
All expressions default to "val".
Some examples follow:
# negate input video
lutrgb="r=maxval+minval-val:g=maxval+minval-val:b=maxval+minval-val"
lutyuv="y=maxval+minval-val:u=maxval+minval-val:v=maxval+minval-val"
# the above is the same as
lutrgb="r=negval:g=negval:b=negval"
lutyuv="y=negval:u=negval:v=negval"
# negate luminance
lutyuv=negval
# remove chroma components, turns the video into a graytone image
lutyuv="u=128:v=128"
# apply a luma burning effect
lutyuv="y=2*val"
# remove green and blue components
lutrgb="g=0:b=0"
# set a constant alpha channel value on input
format=rgba,lutrgb=a="maxval-minval/2"
# correct luminance gamma by a 0.5 factor
lutyuv=y=gammaval(0.5)
negate
Negate input video.
This filter accepts an integer in input, if non-zero it negates the
alpha component (if available). The default value in input is 0.
Force libavfilter not to use any of the specified pixel formats for the
input to the next filter.
The filter accepts a list of pixel format names, separated by ":", for
example "yuv420p:monow:rgb24".
Some examples follow:
# force libavfilter to use a format different from "yuv420p" for the
# input to the vflip filter
noformat=yuv420p,vflip
# convert the input video to any of the formats not contained in the list
noformat=yuv420p:yuv444p:yuv410p
null
Pass the video source unchanged to the output.
ocv
Apply video transform using libopencv.
To enable this filter install libopencv library and headers and
configure Libav with --enable-libopencv.
The filter takes the parameters: filter_name{:=}filter_params.
filter_name is the name of the libopencv filter to apply.
filter_params specifies the parameters to pass to the libopencv filter.
If not specified the default values are assumed.
Refer to the official libopencv documentation for more precise
information:
<http://opencv.willowgarage.com/documentation/c/image_filtering.html>
Follows the list of supported libopencv filters.
dilate
Dilate an image by using a specific structuring element. This filter
corresponds to the libopencv function "cvDilate".
It accepts the parameters: struct_el:nb_iterations.
struct_el represents a structuring element, and has the syntax:
colsxrows+anchor_xxanchor_y/shape
cols and rows represent the number of columns and rows of the
structuring element, anchor_x and anchor_y the anchor point, and shape
the shape for the structuring element, and can be one of the values
"rect", "cross", "ellipse", "custom".
If the value for shape is "custom", it must be followed by a string of
the form "=filename". The file with name filename is assumed to
represent a binary image, with each printable character corresponding
to a bright pixel. When a custom shape is used, cols and rows are
ignored, the number or columns and rows of the read file are assumed
instead.
The default value for struct_el is "3x3+0x0/rect".
nb_iterations specifies the number of times the transform is applied to
the image, and defaults to 1.
Follow some example:
# use the default values
ocv=dilate
# dilate using a structuring element with a 5x5 cross, iterate two times
ocv=dilate=5x5+2x2/cross:2
# read the shape from the file diamond.shape, iterate two times
# the file diamond.shape may contain a pattern of characters like this:
# *
# ***
# *****
# ***
# *
# the specified cols and rows are ignored (but not the anchor point coordinates)
ocv=0x0+2x2/custom=diamond.shape:2
erode
Erode an image by using a specific structuring element. This filter
corresponds to the libopencv function "cvErode".
The filter accepts the parameters: struct_el:nb_iterations, with the
same syntax and semantics as the dilate filter.
smooth
Smooth the input video.
The filter takes the following parameters:
type:param1:param2:param3:param4.
type is the type of smooth filter to apply, and can be one of the
following values: "blur", "blur_no_scale", "median", "gaussian",
"bilateral". The default value is "gaussian".
param1, param2, param3, and param4 are parameters whose meanings depend
on smooth type. param1 and param2 accept integer positive values or 0,
param3 and param4 accept float values.
The default value for param1 is 3, the default value for the other
parameters is 0.
These parameters correspond to the parameters assigned to the libopencv
function "cvSmooth".
overlay
Overlay one video on top of another.
It takes two inputs and one output, the first input is the "main" video
on which the second input is overlayed.
It accepts the parameters: x:y.
x is the x coordinate of the overlayed video on the main video, y is
the y coordinate. The parameters are expressions containing the
following parameters:
main_w, main_h
main input width and height
W, H
same as main_w and main_h
overlay_w, overlay_h
overlay input width and height
w, h
same as overlay_w and overlay_h
Be aware that frames are taken from each input video in timestamp
order, hence, if their initial timestamps differ, it is a a good idea
to pass the two inputs through a setpts=PTS-STARTPTS filter to have
them begin in the same zero timestamp, as it does the example for the
movie filter.
Follow some examples:
# draw the overlay at 10 pixels from the bottom right
# corner of the main video.
overlay=main_w-overlay_w-10:main_h-overlay_h-10
# insert a transparent PNG logo in the bottom left corner of the input
movie=logo.png [logo];
[in][logo] overlay=10:main_h-overlay_h-10 [out]
# insert 2 different transparent PNG logos (second logo on bottom
# right corner):
movie=logo1.png [logo1];
movie=logo2.png [logo2];
[in][logo1] overlay=10:H-h-10 [in+logo1];
[in+logo1][logo2] overlay=W-w-10:H-h-10 [out]
# add a transparent color layer on top of the main video,
# WxH specifies the size of the main input to the overlay filter
color=red.3:WxH [over]; [in][over] overlay [out]
You can chain together more overlays but the efficiency of such
approach is yet to be tested.
pad
Add paddings to the input image, and places the original input at the
given coordinates x, y.
It accepts the following parameters: width:height:x:y:color.
The parameters width, height, x, and y are expressions containing the
following constants:
E, PI, PHI
the corresponding mathematical approximated values for e (euler
number), pi (greek PI), phi (golden ratio)
in_w, in_h
the input video width and height
iw, ih
same as in_w and in_h
out_w, out_h
the output width and height, that is the size of the padded area as
specified by the width and height expressions
ow, oh
same as out_w and out_h
x, y
x and y offsets as specified by the x and y expressions, or NAN if
not yet specified
a input display aspect ratio, same as iw / ih
hsub, vsub
horizontal and vertical chroma subsample values. For example for
the pixel format "yuv422p" hsub is 2 and vsub is 1.
Follows the description of the accepted parameters.
width, height
Specify the size of the output image with the paddings added. If
the value for width or height is 0, the corresponding input size is
used for the output.
The width expression can reference the value set by the height
expression, and vice versa.
The default value of width and height is 0.
x, y
Specify the offsets where to place the input image in the padded
area with respect to the top/left border of the output image.
The x expression can reference the value set by the y expression,
and vice versa.
The default value of x and y is 0.
color
Specify the color of the padded area, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence.
The default value of color is "black".
Some examples follow:
# Add paddings with color "violet" to the input video. Output video
# size is 640x480, the top-left corner of the input video is placed at
# column 0, row 40.
pad=640:480:0:40:violet
# pad the input to get an output with dimensions increased bt 3/2,
# and put the input video at the center of the padded area
pad="3/2*iw:3/2*ih:(ow-iw)/2:(oh-ih)/2"
# pad the input to get a squared output with size equal to the maximum
# value between the input width and height, and put the input video at
# the center of the padded area
pad="max(iw,ih):ow:(ow-iw)/2:(oh-ih)/2"
# pad the input to get a final w/h ratio of 16:9
pad="ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"
# double output size and put the input video in the bottom-right
# corner of the output padded area
pad="2*iw:2*ih:ow-iw:oh-ih"
pixdesctest
Pixel format descriptor test filter, mainly useful for internal
testing. The output video should be equal to the input video.
For example:
format=monow, pixdesctest
can be used to test the monowhite pixel format descriptor definition.
scale
Scale the input video to width:height and/or convert the image format.
The parameters width and height are expressions containing the
following constants:
E, PI, PHI
the corresponding mathematical approximated values for e (euler
number), pi (greek PI), phi (golden ratio)
in_w, in_h
the input width and height
iw, ih
same as in_w and in_h
out_w, out_h
the output (cropped) width and height
ow, oh
same as out_w and out_h
dar, a
input display aspect ratio, same as iw / ih
sar input sample aspect ratio
hsub, vsub
horizontal and vertical chroma subsample values. For example for
the pixel format "yuv422p" hsub is 2 and vsub is 1.
If the input image format is different from the format requested by the
next filter, the scale filter will convert the input to the requested
format.
If the value for width or height is 0, the respective input size is
used for the output.
If the value for width or height is -1, the scale filter will use, for
the respective output size, a value that maintains the aspect ratio of
the input image.
The default value of width and height is 0.
Some examples follow:
# scale the input video to a size of 200x100.
scale=200:100
# scale the input to 2x
scale=2*iw:2*ih
# the above is the same as
scale=2*in_w:2*in_h
# scale the input to half size
scale=iw/2:ih/2
# increase the width, and set the height to the same size
scale=3/2*iw:ow
# seek for Greek harmony
scale=iw:1/PHI*iw
scale=ih*PHI:ih
# increase the height, and set the width to 3/2 of the height
scale=3/2*oh:3/5*ih
# increase the size, but make the size a multiple of the chroma
scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"
# increase the width to a maximum of 500 pixels, keep the same input aspect ratio
scale='min(500, iw*3/2):-1'
select
Select frames to pass in output.
It accepts in input an expression, which is evaluated for each input
frame. If the expression is evaluated to a non-zero value, the frame is
selected and passed to the output, otherwise it is discarded.
The expression can contain the following constants:
PI Greek PI
PHI golden ratio
E Euler number
n the sequential number of the filtered frame, starting from 0
selected_n
the sequential number of the selected frame, starting from 0
prev_selected_n
the sequential number of the last selected frame, NAN if undefined
TB timebase of the input timestamps
pts the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in TB units, NAN if undefined
t the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in seconds, NAN if undefined
prev_pts
the PTS of the previously filtered video frame, NAN if undefined
prev_selected_pts
the PTS of the last previously filtered video frame, NAN if
undefined
prev_selected_t
the PTS of the last previously selected video frame, NAN if
undefined
start_pts
the PTS of the first video frame in the video, NAN if undefined
start_t
the time of the first video frame in the video, NAN if undefined
pict_type
the type of the filtered frame, can assume one of the following
values:
I
P
B
S
SI
SP
BI
interlace_type
the frame interlace type, can assume one of the following values:
PROGRESSIVE
the frame is progressive (not interlaced)
TOPFIRST
the frame is top-field-first
BOTTOMFIRST
the frame is bottom-field-first
key 1 if the filtered frame is a key-frame, 0 otherwise
pos the position in the file of the filtered frame, -1 if the
information is not available (e.g. for synthetic video)
The default value of the select expression is "1".
Some examples follow:
# select all frames in input
select
# the above is the same as:
select=1
# skip all frames:
select=0
# select only I-frames
select='eq(pict_type,I)'
# select one frame every 100
select='not(mod(n,100))'
# select only frames contained in the 10-20 time interval
select='gte(t,10)*lte(t,20)'
# select only I frames contained in the 10-20 time interval
select='gte(t,10)*lte(t,20)*eq(pict_type,I)'
# select frames with a minimum distance of 10 seconds
select='isnan(prev_selected_t)+gte(t-prev_selected_t,10)'
setdar
Set the Display Aspect Ratio for the filter output video.
This is done by changing the specified Sample (aka Pixel) Aspect Ratio,
according to the following equation: DAR = HORIZONTAL_RESOLUTION /
VERTICAL_RESOLUTION * SAR
Keep in mind that this filter does not modify the pixel dimensions of
the video frame. Also the display aspect ratio set by this filter may
be changed by later filters in the filterchain, e.g. in case of scaling
or if another "setdar" or a "setsar" filter is applied.
The filter accepts a parameter string which represents the wanted
display aspect ratio. The parameter can be a floating point number
string, or an expression of the form num:den, where num and den are the
numerator and denominator of the aspect ratio. If the parameter is not
specified, it is assumed the value "0:1".
For example to change the display aspect ratio to 16:9, specify:
setdar=16:9
# the above is equivalent to
setdar=1.77777
See also the setsar filter documentation.
setpts
Change the PTS (presentation timestamp) of the input video frames.
Accept in input an expression evaluated through the eval API, which can
contain the following constants:
PTS the presentation timestamp in input
PI Greek PI
PHI golden ratio
E Euler number
N the count of the input frame, starting from 0.
STARTPTS
the PTS of the first video frame
INTERLACED
tell if the current frame is interlaced
POS original position in the file of the frame, or undefined if
undefined for the current frame
PREV_INPTS
previous input PTS
PREV_OUTPTS
previous output PTS
Some examples follow:
# start counting PTS from zero
setpts=PTS-STARTPTS
# fast motion
setpts=0.5*PTS
# slow motion
setpts=2.0*PTS
# fixed rate 25 fps
setpts=N/(25*TB)
# fixed rate 25 fps with some jitter
setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))'
setsar
Set the Sample (aka Pixel) Aspect Ratio for the filter output video.
Note that as a consequence of the application of this filter, the
output display aspect ratio will change according to the following
equation: DAR = HORIZONTAL_RESOLUTION / VERTICAL_RESOLUTION * SAR
Keep in mind that the sample aspect ratio set by this filter may be
changed by later filters in the filterchain, e.g. if another "setsar"
or a "setdar" filter is applied.
The filter accepts a parameter string which represents the wanted
sample aspect ratio. The parameter can be a floating point number
string, or an expression of the form num:den, where num and den are the
numerator and denominator of the aspect ratio. If the parameter is not
specified, it is assumed the value "0:1".
For example to change the sample aspect ratio to 10:11, specify:
setsar=10:11
settb
Set the timebase to use for the output frames timestamps. It is mainly
useful for testing timebase configuration.
It accepts in input an arithmetic expression representing a rational.
The expression can contain the constants "PI", "E", "PHI", "AVTB" (the
default timebase), and "intb" (the input timebase).
The default value for the input is "intb".
Follow some examples.
# set the timebase to 1/25
settb=1/25
# set the timebase to 1/10
settb=0.1
#set the timebase to 1001/1000
settb=1+0.001
#set the timebase to 2*intb
settb=2*intb
#set the default timebase value
settb=AVTB
showinfo
Show a line containing various information for each input video frame.
The input video is not modified.
The shown line contains a sequence of key/value pairs of the form
key:value.
A description of each shown parameter follows:
n sequential number of the input frame, starting from 0
pts Presentation TimeStamp of the input frame, expressed as a number of
time base units. The time base unit depends on the filter input
pad.
pts_time
Presentation TimeStamp of the input frame, expressed as a number of
seconds
pos position of the frame in the input stream, -1 if this information
in unavailable and/or meaningless (for example in case of synthetic
video)
fmt pixel format name
sar sample aspect ratio of the input frame, expressed in the form
num/den
s size of the input frame, expressed in the form widthxheight
i interlaced mode ("P" for "progressive", "T" for top field first,
"B" for bottom field first)
iskey
1 if the frame is a key frame, 0 otherwise
type
picture type of the input frame ("I" for an I-frame, "P" for a
P-frame, "B" for a B-frame, "?" for unknown type). Check also the
documentation of the "AVPictureType" enum and of the
"av_get_picture_type_char" function defined in libavutil/avutil.h.
checksum
Adler-32 checksum of all the planes of the input frame
plane_checksum
Adler-32 checksum of each plane of the input frame, expressed in
the form "[c0 c1 c2 c3]"
slicify
Pass the images of input video on to next video filter as multiple
slices.
./avconv -i in.avi -vf "slicify=32" out.avi
The filter accepts the slice height as parameter. If the parameter is
not specified it will use the default value of 16.
Adding this in the beginning of filter chains should make filtering
faster due to better use of the memory cache.
transpose
Transpose rows with columns in the input video and optionally flip it.
It accepts a parameter representing an integer, which can assume the
values:
0 Rotate by 90 degrees counterclockwise and vertically flip
(default), that is:
L.R L.l
. . -> . .
l.r R.r
1 Rotate by 90 degrees clockwise, that is:
L.R l.L
. . -> . .
l.r r.R
2 Rotate by 90 degrees counterclockwise, that is:
L.R R.r
. . -> . .
l.r L.l
3 Rotate by 90 degrees clockwise and vertically flip, that is:
L.R r.R
. . -> . .
l.r l.L
unsharp
Sharpen or blur the input video.
It accepts the following parameters:
luma_msize_x:luma_msize_y:luma_amount:chroma_msize_x:chroma_msize_y:chroma_amount
Negative values for the amount will blur the input video, while
positive values will sharpen. All parameters are optional and default
to the equivalent of the string '5:5:1.0:5:5:0.0'.
luma_msize_x
Set the luma matrix horizontal size. It can be an integer between 3
and 13, default value is 5.
luma_msize_y
Set the luma matrix vertical size. It can be an integer between 3
and 13, default value is 5.
luma_amount
Set the luma effect strength. It can be a float number between -2.0
and 5.0, default value is 1.0.
chroma_msize_x
Set the chroma matrix horizontal size. It can be an integer between
3 and 13, default value is 5.
chroma_msize_y
Set the chroma matrix vertical size. It can be an integer between 3
and 13, default value is 5.
luma_amount
Set the chroma effect strength. It can be a float number between
-2.0 and 5.0, default value is 0.0.
# Strong luma sharpen effect parameters
unsharp=7:7:2.5
# Strong blur of both luma and chroma parameters
unsharp=7:7:-2:7:7:-2
# Use the default values with B<avconv>
./avconv -i in.avi -vf "unsharp" out.mp4
vflip
Flip the input video vertically.
./avconv -i in.avi -vf "vflip" out.avi
yadif
Deinterlace the input video ("yadif" means "yet another deinterlacing
filter").
It accepts the optional parameters: mode:parity:auto.
mode specifies the interlacing mode to adopt, accepts one of the
following values:
0 output 1 frame for each frame
1 output 1 frame for each field
2 like 0 but skips spatial interlacing check
3 like 1 but skips spatial interlacing check
Default value is 0.
parity specifies the picture field parity assumed for the input
interlaced video, accepts one of the following values:
0 assume top field first
1 assume bottom field first
-1 enable automatic detection
Default value is -1. If interlacing is unknown or decoder does not
export this information, top field first will be assumed.
auto specifies if deinterlacer should trust the interlaced flag and
only deinterlace frames marked as interlaced
0 deinterlace all frames
1 only deinterlace frames marked as interlaced
Default value is 0.
VIDEO SOURCES
Below is a description of the currently available video sources.
buffer
Buffer video frames, and make them available to the filter chain.
This source is mainly intended for a programmatic use, in particular
through the interface defined in libavfilter/vsrc_buffer.h.
It accepts the following parameters:
width:height:pix_fmt_string:timebase_num:timebase_den:sample_aspect_ratio_num:sample_aspect_ratio.den
All the parameters need to be explicitly defined.
Follows the list of the accepted parameters.
width, height
Specify the width and height of the buffered video frames.
pix_fmt_string
A string representing the pixel format of the buffered video
frames. It may be a number corresponding to a pixel format, or a
pixel format name.
timebase_num, timebase_den
Specify numerator and denomitor of the timebase assumed by the
timestamps of the buffered frames.
sample_aspect_ratio.num, sample_aspect_ratio.den
Specify numerator and denominator of the sample aspect ratio
assumed by the video frames.
For example:
buffer=320:240:yuv410p:1:24:1:1
will instruct the source to accept video frames with size 320x240 and
with format "yuv410p", assuming 1/24 as the timestamps timebase and
square pixels (1:1 sample aspect ratio). Since the pixel format with
name "yuv410p" corresponds to the number 6 (check the enum PixelFormat
definition in libavutil/pixfmt.h), this example corresponds to:
buffer=320:240:6:1:24
color
Provide an uniformly colored input.
It accepts the following parameters: color:frame_size:frame_rate
Follows the description of the accepted parameters.
color
Specify the color of the source. It can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence, possibly
followed by an alpha specifier. The default value is "black".
frame_size
Specify the size of the sourced video, it may be a string of the
form widthxheight, or the name of a size abbreviation. The default
value is "320x240".
frame_rate
Specify the frame rate of the sourced video, as the number of
frames generated per second. It has to be a string in the format
frame_rate_num/frame_rate_den, an integer number, a float number or
a valid video frame rate abbreviation. The default value is "25".
For example the following graph description will generate a red source
with an opacity of 0.2, with size "qcif" and a frame rate of 10 frames
per second, which will be overlayed over the source connected to the
pad with identifier "in".
"color=red@0.2:qcif:10 [color]; [in][color] overlay [out]"
movie
Read a video stream from a movie container.
It accepts the syntax: movie_name[:options] where movie_name is the
name of the resource to read (not necessarily a file but also a device
or a stream accessed through some protocol), and options is an optional
sequence of key=value pairs, separated by ":".
The description of the accepted options follows.
format_name, f
Specifies the format assumed for the movie to read, and can be
either the name of a container or an input device. If not specified
the format is guessed from movie_name or by probing.
seek_point, sp
Specifies the seek point in seconds, the frames will be output
starting from this seek point, the parameter is evaluated with
"av_strtod" so the numerical value may be suffixed by an IS
postfix. Default value is "0".
stream_index, si
Specifies the index of the video stream to read. If the value is
-1, the best suited video stream will be automatically selected.
Default value is "-1".
This filter allows to overlay a second video on top of main input of a
filtergraph as shown in this graph:
input -----------> deltapts0 --> overlay --> output
^
|
movie --> scale--> deltapts1 -------+
Some examples follow:
# skip 3.2 seconds from the start of the avi file in.avi, and overlay it
# on top of the input labelled as "in".
movie=in.avi:seek_point=3.2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]
# read from a video4linux2 device, and overlay it on top of the input
# labelled as "in"
movie=/dev/video0:f=video4linux2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]
nullsrc
Null video source, never return images. It is mainly useful as a
template and to be employed in analysis / debugging tools.
It accepts as optional parameter a string of the form
width:height:timebase.
width and height specify the size of the configured source. The default
values of width and height are respectively 352 and 288 (corresponding
to the CIF size format).
timebase specifies an arithmetic expression representing a timebase.
The expression can contain the constants "PI", "E", "PHI", "AVTB" (the
default timebase), and defaults to the value "AVTB".
frei0r_src
Provide a frei0r source.
To enable compilation of this filter you need to install the frei0r
header and configure Libav with --enable-frei0r.
The source supports the syntax:
<size>:<rate>:<src_name>[{=|:}<param1>:<param2>:...:<paramN>]
size is the size of the video to generate, may be a string of the form
widthxheight or a frame size abbreviation. rate is the rate of the
video to generate, may be a string of the form num/den or a frame rate
abbreviation. src_name is the name to the frei0r source to load. For
more information regarding frei0r and how to set the parameters read
the section frei0r in the description of the video filters.
Some examples follow:
# generate a frei0r partik0l source with size 200x200 and framerate 10
# which is overlayed on the overlay filter main input
frei0r_src=200x200:10:partik0l=1234 [overlay]; [in][overlay] overlay
rgbtestsrc, testsrc
The "rgbtestsrc" source generates an RGB test pattern useful for
detecting RGB vs BGR issues. You should see a red, green and blue
stripe from top to bottom.
The "testsrc" source generates a test video pattern, showing a color
pattern, a scrolling gradient and a timestamp. This is mainly intended
for testing purposes.
Both sources accept an optional sequence of key=value pairs, separated
by ":". The description of the accepted options follows.
size, s
Specify the size of the sourced video, it may be a string of the
form widthxheight, or the name of a size abbreviation. The default
value is "320x240".
rate, r
Specify the frame rate of the sourced video, as the number of
frames generated per second. It has to be a string in the format
frame_rate_num/frame_rate_den, an integer number, a float number or
a valid video frame rate abbreviation. The default value is "25".
sar Set the sample aspect ratio of the sourced video.
duration
Set the video duration of the sourced video. The accepted syntax
is:
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
See also the function "av_parse_time()".
If not specified, or the expressed duration is negative, the video
is supposed to be generated forever.
For example the following:
testsrc=duration=5.3:size=qcif:rate=10
will generate a video with a duration of 5.3 seconds, with size 176x144
and a framerate of 10 frames per second.
VIDEO SINKS
Below is a description of the currently available video sinks.
nullsink
Null video sink, do absolutely nothing with the input video. It is
mainly useful as a template and to be employed in analysis / debugging
tools.
METADATA
Libav is able to dump metadata from media files into a simple
UTF-8-encoded INI-like text file and then load it back using the
metadata muxer/demuxer.
The file format is as follows:
1. A file consists of a header and a number of metadata tags divided
into sections, each on its own line.
2. The header is a ';FFMETADATA' string, followed by a version number
(now 1).
3. Metadata tags are of the form 'key=value'
4. Immediately after header follows global metadata
5. After global metadata there may be sections with
per-stream/per-chapter metadata.
6. A section starts with the section name in uppercase (i.e. STREAM or
CHAPTER) in brackets ('[', ']') and ends with next section or end
of file.
7. At the beginning of a chapter section there may be an optional
timebase to be used for start/end values. It must be in form
'TIMEBASE=num/den', where num and den are integers. If the timebase
is missing then start/end times are assumed to be in milliseconds.
Next a chapter section must contain chapter start and end times in
form 'START=num', 'END=num', where num is a positive integer.
8. Empty lines and lines starting with ';' or '#' are ignored.
9. Metadata keys or values containing special characters ('=', ';',
'#', '\' and a newline) must be escaped with a backslash '\'.
10. Note that whitespace in metadata (e.g. foo = bar) is considered to
be a part of the tag (in the example above key is 'foo ', value is
' bar').
A ffmetadata file might look like this:
;FFMETADATA1
title=bike\\shed
;this is a comment
artist=Libav troll team
[CHAPTER]
TIMEBASE=1/1000
START=0
#chapter ends at 0:01:00
END=60000
title=chapter \#1
[STREAM]
title=multi\
line
SEE ALSOavplay(1), avprobe(1) and the Libav HTML documentation
AUTHORS
The Libav developers
2013-05-20 AVCONV(1)
