[trans] FFMPEG Document

FFmpeg Documentation

 

 

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Table of Contents

• 1. Synopsis
• 2. Description
• 3. Options
  • 3.1 Generic options
  • 3.2 Main options
  • 3.3 Video Options
  • 3.4 Advanced Video Options
  • 3.5 Audio Options
  • 3.6 Advanced Audio options:
  • 3.7 Subtitle options:
  • 3.8 Audio/Video grab options
  • 3.9 Advanced options
  • 3.10 Preset files
• 4. Tips
• 5. Examples
  • 5.1 Video and Audio grabbing
  • 5.2 X11 grabbing
  • 5.3 Video and Audio file format conversion
• 6. Expression Evaluation
• 7. Input Devices
  • 7.1 alsa
  • 7.2 bktr
  • 7.3 dv1394
  • 7.4 jack
  • 7.5 libdc1394
  • 7.6 oss
  • 7.7 video4linux and video4linux2
  • 7.8 vfwcap
  • 7.9 x11grab
• 8. Output Devices
  • 8.1 alsa
  • 8.2 oss
• 9. Protocols
  • 9.1 concat
  • 9.2 file
  • 9.3 gopher
  • 9.4 http
  • 9.5 mmst
  • 9.6 mmsh
  • 9.7 md5
  • 9.8 pipe
  • 9.9 rtmp
  • 9.10 rtmp, rtmpe, rtmps, rtmpt, rtmpte
  • 9.11 rtp
  • 9.12 rtsp
  • 9.13 sap
    • 9.13.1 Muxer
    • 9.13.2 Demuxer
  • 9.14 tcp
  • 9.15 udp
• 10. Bitstream Filters
  • 10.1 aac_adtstoasc
  • 10.2 chomp
  • 10.3 dump_extradata
  • 10.4 h264_mp4toannexb
  • 10.5 imx_dump_header
  • 10.6 mjpeg2jpeg
  • 10.7 mjpega_dump_header
  • 10.8 movsub
  • 10.9 mp3_header_compress
  • 10.10 mp3_header_decompress
  • 10.11 noise
  • 10.12 remove_extradata
• 11. Filtergraph description
  • 11.1 Filtergraph syntax
• 12. Audio Filters
  • 12.1 anull
• 13. Audio Sources
  • 13.1 anullsrc
• 14. Audio Sinks
  • 14.1 anullsink
• 15. Video Filters
  • 15.1 blackframe
  • 15.2 crop
  • 15.3 cropdetect
  • 15.4 drawbox
  • 15.5 fifo
  • 15.6 format
  • 15.7 frei0r
  • 15.8 gradfun
  • 15.9 hflip
  • 15.10 hqdn3d
  • 15.11 noformat
  • 15.12 null
  • 15.13 ocv_smooth
  • 15.14 overlay
  • 15.15 pad
  • 15.16 pixdesctest
  • 15.17 scale
  • 15.18 setpts
  • 15.19 settb
  • 15.20 slicify
  • 15.21 transpose
  • 15.22 unsharp
  • 15.23 vflip
  • 15.24 yadif
• 16. Video Sources
  • 16.1 buffer
  • 16.2 color
  • 16.3 nullsrc
  • 16.4 frei0r_src
• 17. Video Sinks
  • 17.1 nullsink

 

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FFmpeg Documentation

1. Synopsis

The generic syntax is:

ffmpeg [[infile options][`-i' infile]]... {[outfile options] outfile}...

2. Description

FFmpeg is a very fast video and audio converter. It can also grab from a live audio/video source.

The command line interface is designed to be intuitive, in the sense that FFmpeg tries to figure out all parameters that can possibly be derived automatically. You usually only have to specify the target bitrate you want.

FFmpeg can also convert from any sample rate to any other, and resize video on the fly with a high quality polyphase filter.

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.

* To set the video bitrate of the output file to 64kbit/s:

ffmpeg -i input.avi -b 64k output.avi

* To force the frame rate of the output file to 24 fps:

ffmpeg -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:

ffmpeg -r 1 -i input.m2v -r 24 output.avi

The format option may be needed for raw input files.

By default, FFmpeg tries to convert as losslessly as possible: It uses the same audio and video parameters for the outputs as the one specified for the inputs.

3. 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 commandline will set to false the boolean option with name "foo".

3.1 Generic options

These options are shared amongst the ff* 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.

`-loglevel 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 @env{FFMPEG_FORCE_NOCOLOR} or @env{NO_COLOR}, or can be forced setting the environment variable @env{FFMPEG_FORCE_COLOR}. The use of the environment variable @env{NO_COLOR} is deprecated and will be dropped in a following FFmpeg version.

3.2 Main options

`-f fmt'

Force format.

`-i filename'

input file name

`-y'

Overwrite output files.

`-t duration'

Restrict the transcoded/captured video sequence to the duration specified in seconds. hh:mm:ss[.xxx] syntax is also supported.

`-fs limit_size'

Set the file size limit.

`-ss position'

Seek to given time position in seconds. hh:mm:ss[.xxx] syntax is also supported.

`-itsoffset offset'

Set the input time offset in seconds. [-]hh:mm:ss[.xxx] syntax is also supported. This option affects all the input files that follow it. 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.

`-timestamp time'

Set the recording timestamp in the container. The syntax for time is:

now|([(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH[:MM[:SS[.m...]]])|(HH[MM[SS[.m...]]]))[Z|z])

If the value is "now" it takes the current time. Time is local time unless 'Z' or 'z' is appended, in which case it is interpreted as UTC. If the year-month-day part is not specified it takes the current year-month-day.

`-metadata key=value'

Set a metadata key/value pair. For example, for setting the title in the output file:

ffmpeg -i in.avi -metadata title="my title" out.flv

`-v number'

Set the logging verbosity level.

`-target type'

Specify target file type ("vcd", "svcd", "dvd", "dv", "dv50", "pal-vcd", "ntsc-svcd", ... ). All the format options (bitrate, codecs, buffer sizes) are then set automatically. You can just type:

ffmpeg -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:

ffmpeg -i myfile.avi -target vcd -bf 2 /tmp/vcd.mpg

`-dframes number'

Set the number of data frames to record.

`-scodec codec'

Force subtitle codec ('copy' to copy stream).

`-newsubtitle'

Add a new subtitle stream to the current output stream.

`-slang code'

Set the ISO 639 language code (3 letters) of the current subtitle stream.

3.3 Video Options

`-b bitrate'

Set the video bitrate in bit/s (default = 200 kb/s).

`-vframes number'

Set the number of video frames to record.

`-r fps'

Set frame rate (Hz value, fraction or abbreviation), (default = 25).

`-s size'

Set frame size. The format is `wxh' (ffserver default = 160x128, ffmpeg 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 aspect'

Set aspect ratio (4:3, 16:9 or 1.3333, 1.7777).

`-croptop size'

`-cropbottom size'

`-cropleft size'

`-cropright size'

All the crop options have been removed. Use -vf crop=width:height:x:y instead.

`-padtop size'

`-padbottom size'

`-padleft size'

`-padright size'

`-padcolor hex_color'

All the pad options have been removed. Use -vf pad=width:height:x:y:color instead.

`-vn'

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:

ffmpeg -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'

Force video codec to codec. Use the copy special value to tell that the raw codec data must be copied as is.

`-sameq'

Use same video quality as source (implies VBR).

`-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:

ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y NUL
ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y /dev/null

`-passlogfile prefix'

Set two-pass log file name prefix to prefix, the default file name prefix is "ffmpeg2pass". The complete file name will be `PREFIX-N.log', where N is a number specific to the output stream.

`-newvideo'

Add a new video stream to the current output stream.

`-vlang code'

Set the ISO 639 language code (3 letters) of the current video stream.

`-vf filter_graph'

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).

3.4 Advanced Video Options

`-pix_fmt format'

Set pixel format. Use 'list' as parameter to show all the supported pixel formats.

`-sws_flags flags'

Set SwScaler flags.

`-g gop_size'

Set the group of pictures size.

`-intra'

Use only intra frames.

`-vdt n'

Discard threshold.

`-qscale q'

Use fixed video quantizer scale (VBR).

`-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:

ffmpeg -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 override'

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)

`-dct_algo algo'

Set DCT algorithm to algo. Available values are:

`0'

FF_DCT_AUTO (default)

`1'

FF_DCT_FASTINT

`2'

FF_DCT_INT

`3'

FF_DCT_MMX

`4'

FF_DCT_MLIB

`5'

FF_DCT_ALTIVEC

`-idct_algo algo'

Set IDCT algorithm to algo. Available values are:

`0'

FF_IDCT_AUTO (default)

`1'

FF_IDCT_INT

`2'

FF_IDCT_SIMPLE

`3'

FF_IDCT_SIMPLEMMX

`4'

FF_IDCT_LIBMPEG2MMX

`5'

FF_IDCT_PS2

`6'

FF_IDCT_MLIB

`7'

FF_IDCT_ARM

`8'

FF_IDCT_ALTIVEC

`9'

FF_IDCT_SH4

`10'

FF_IDCT_SIMPLEARM

`-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 FFmpeg).

`1'

FF_MB_DECISION_BITS: Choose the one which needs the fewest bits.

`2'

FF_MB_DECISION_RD: rate distortion

`-4mv'

Use four motion vector by macroblock (MPEG-4 only).

`-part'

Use data partitioning (MPEG-4 only).

`-bug param'

Work around encoder bugs that are not auto-detected.

`-strict strictness'

How strictly to follow the standards.

`-aic'

Enable Advanced intra coding (h263+).

`-umv'

Enable Unlimited Motion Vector (h263+)

`-deinterlace'

Deinterlace pictures.

`-ilme'

Force interlacing support in encoder (MPEG-2 and MPEG-4 only). Use this option if your input file is interlaced and you want to keep the interlaced format for minimum losses. The alternative is to deinterlace the input stream with `-deinterlace', but deinterlacing introduces losses.

`-psnr'

Calculate PSNR of compressed frames.

`-vstats'

Dump video coding statistics to `vstats_HHMMSS.log'.

`-vstats_file file'

Dump video coding statistics to file.

`-top n'

top=1/bottom=0/auto=-1 field first

`-dc precision'

Intra_dc_precision.

`-vtag fourcc/tag'

Force video tag/fourcc.

`-qphist'

Show QP histogram.

`-vbsf bitstream_filter'

Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump", "mjpeg2jpeg".

ffmpeg -i h264.mp4 -vcodec copy -vbsf h264_mp4toannexb -an out.h264

`-force_key_frames time[,time...]'

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.

3.5 Audio Options

`-aframes number'

Set the number of audio frames to record.

`-ar freq'

Set the audio sampling frequency (default = 44100 Hz).

`-ab bitrate'

Set the audio bitrate in bit/s (default = 64k).

`-aq q'

Set the audio quality (codec-specific, VBR).

`-ac channels'

Set the number of audio channels. For input streams it is set by default to 1, for output streams it is set by default to the same number of audio channels in input. If the input file has audio streams with different channel count, the behaviour is undefined.

`-an'

Disable audio recording.

`-acodec codec'

Force audio codec to codec. Use the copy special value to specify that the raw codec data must be copied as is.

`-newaudio'

Add a new audio track to the output file. If you want to specify parameters, do so before -newaudio (-acodec, -ab, etc..). Mapping will be done automatically, if the number of output streams is equal to the number of input streams, else it will pick the first one that matches. You can override the mapping using -map as usual. Example:

ffmpeg -i file.mpg -vcodec copy -acodec ac3 -ab 384k test.mpg -acodec mp2 -ab 192k -newaudio

`-alang code'

Set the ISO 639 language code (3 letters) of the current audio stream.

3.6 Advanced Audio options:

`-atag fourcc/tag'

Force audio tag/fourcc.

`-absf bitstream_filter'

Bitstream filters available are "dump_extra", "remove_extra", "noise", "mp3comp", "mp3decomp".

3.7 Subtitle options:

`-scodec codec'

Force subtitle codec ('copy' to copy stream).

`-newsubtitle'

Add a new subtitle stream to the current output stream.

`-slang code'

Set the ISO 639 language code (3 letters) of the current subtitle stream.

`-sn'

Disable subtitle recording.

`-sbsf bitstream_filter'

Bitstream filters available are "mov2textsub", "text2movsub".

ffmpeg -i file.mov -an -vn -sbsf mov2textsub -scodec copy -f rawvideo sub.txt

3.8 Audio/Video grab options

`-vc channel'

Set video grab channel (DV1394 only).

`-tvstd standard'

Set television standard (NTSC, PAL (SECAM)).

`-isync'

Synchronize read on input.

3.9 Advanced options

`-map input_stream_id[:sync_stream_id]'

Set stream mapping from input streams to output streams. Just enumerate the input streams in the order you want them in the output. sync_stream_id if specified sets the input stream to sync against.

`-map_meta_data outfile[,metadata]:infile[,metadata]'

Set meta data information of outfile from infile. Note that those are file indices (zero-based), not filenames. Optional metadata parameters specify, which metadata to copy - (g)lobal (i.e. metadata that applies to the whole file), per-(s)tream, per-(c)hapter or per-(p)rogram. All metadata specifiers other than global must be followed by the stream/chapter/program number. If metadata specifier is omitted, it defaults to global. By default, global metadata is copied from the first input file to all output files, 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:

ffmpeg -i in.ogg -map_meta_data 0:0,s0 out.mp3

`-map_chapters outfile:infile'

Copy chapters from infile to outfile. If no chapter mapping is specified, then chapters are copied from the first input file with at least one chapter to all output files. Use a negative file index to disable any chapter copying.

`-debug'

Print specific debug info.

`-benchmark'

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.

`-dump'

Dump each input packet.

`-hex'

When dumping packets, also dump the payload.

`-bitexact'

Only use bit exact algorithms (for codec testing).

`-ps size'

Set RTP payload size in bytes.

`-re'

Read input at native frame rate. Mainly used to simulate a grab device.

`-loop_input'

Loop over the input stream. Currently it works only for image streams. This option is used for automatic FFserver testing.

`-loop_output number_of_times'

Repeatedly loop output for formats that support looping such as animated GIF (0 will loop the output infinitely).

`-threads count'

Thread count.

`-vsync parameter'

Video sync method. 0 Each frame is passed with its timestamp from the demuxer to the muxer 1 Frames will be duplicated and dropped to achieve exactly the requested constant framerate. 2 Frames are passed through with their timestamp or dropped so as to prevent 2 frames from having the same timestamp -1 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.

`-shortest'

Finish encoding when the shortest input stream ends.

`-dts_delta_threshold'

Timestamp discontinuity delta threshold.

`-muxdelay seconds'

Set the maximum demux-decode delay.

`-muxpreload seconds'

Set the initial demux-decode delay.

`-streamid output-stream-index:new-value'

Assign a new value to a stream's stream-id field in the next output file. All stream-id fields are reset to default for each output file. For example, to set the stream 0 PID to 33 and the stream 1 PID to 36 for an output mpegts file:

ffmpeg -i infile -streamid 0:33 -streamid 1:36 out.ts

3.10 Preset files

A preset file contains a sequence of option=value pairs, one for each line, specifying a sequence of options which would be awkward to specify on the command line. Lines starting with the hash ('#') character are ignored and are used to provide comments. Check the `ffpresets' directory in the FFmpeg source tree for examples.

Preset files are specified with the vpre, apre, spre, and fpre options. The fpre option takes the filename of the preset instead of a preset name as input and can be used for any kind of codec. For the vpre, apre, and spre options, the options specified in a preset file are applied to the currently selected codec of the same type as the preset option.

The argument passed to the vpre, apre, and spre preset options identifies the preset file to use according to the following rules:

First ffmpeg searches for a file named arg.ffpreset in the directories `$FFMPEG_DATADIR' (if set), and `$HOME/.ffmpeg', and in the datadir defined at configuration time (usually `PREFIX/share/ffmpeg') in that order. For example, if the argument is libx264-max, it will search for the file `libx264-max.ffpreset'.

If no such file is found, then ffmpeg will search for a file named codec_name-arg.ffpreset in the above-mentioned directories, where codec_name is the name of the codec to which the preset file options will be applied. For example, if you select the video codec with -vcodec libx264 and use -vpre max, then it will search for the file `libx264-max.ffpreset'.

4. 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:

  ffmpeg -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).
• When converting video files, you can use the '-sameq' option which uses the same quality factor in the encoder as in the decoder. It allows almost lossless encoding.

5. Examples

5.1 Video and Audio grabbing

FFmpeg can grab video and audio from devices given that you specify the input format and device.

ffmpeg -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 FFmpeg 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.

5.2 X11 grabbing

FFmpeg can grab the X11 display.

ffmpeg -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.

ffmpeg -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.

5.3 Video and Audio file format conversion

* FFmpeg can use any supported file format and protocol as input:

Examples:

* You can use YUV files as input:

ffmpeg -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 FFmpeg cannot guess it.

* You can input from a raw YUV420P file:

ffmpeg -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:

ffmpeg -i mydivx.avi hugefile.yuv

* You can set several input files and output files:

ffmpeg -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:

ffmpeg -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:

ffmpeg -i /tmp/a.wav -ab 64k /tmp/a.mp2 -ab 128k /tmp/b.mp2 -map 0:0 -map 0:0

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:

ffmpeg -i snatch_1.vob -f avi -vcodec mpeg4 -b 800k -g 300 -bf 2 -acodec libmp3lame -ab 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 ffmpeg -formats.

* You can extract images from a video, or create a video from many images:

For extracting images from a video:

ffmpeg -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:

ffmpeg -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:

ffmpeg -i test1.avi -i test2.avi -vcodec copy -acodec copy -vcodec copy -acodec copy test12.avi -newvideo -newaudio

In addition to the first video and audio streams, the resulting output file `test12.avi' will contain the second video and the second audio stream found in the input streams list.

The -newvideo, -newaudio and -newsubtitle options have to be specified immediately after the name of the output file to which you want to add them.

6. Expression Evaluation

When evaluating an arithemetic expression, FFmpeg 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 previosly 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.

Note that:

* works like AND

+ works like OR

thus

if A then B else C

is equivalent to

A*B + not(A)*C

When A evaluates to either 1 or 0, that is the same as

A*B + eq(A,0)*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

7. Input Devices

Input devices are configured elements in FFmpeg which allow to access the data coming from a multimedia device attached to your system.

When you configure your FFmpeg 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 ff* tools will display the list of supported input devices (amongst the demuxers).

A description of the currently available input devices follows.

7.1 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 `ffmpeg' from an ALSA device with card id 0, you may run the command:

ffmpeg -f alsa -i hw:0 alsaout.wav

For more information see: http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html

7.2 bktr

BSD video input device.

7.3 dv1394

Linux DV 1394 input device.

7.4 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 FFmpeg 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 `ffmpeg'.

# Create a JACK writable client with name "ffmpeg".
$ ffmpeg -f jack -i ffmpeg -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
ffmpeg:input_1
metro:120_bpm

# Connect metro to the ffmpeg writable client.
$ jack_connect metro:120_bpm ffmpeg:input_1

For more information read: http://jackaudio.org/

7.5 libdc1394

IIDC1394 input device, based on libdc1394 and libraw1394.

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