Guide

1. Synopsis

ffmpeg [global_options]
      {[input_file_options] -i input_url} ...
      {[output_file_options] output_url} ...

2. Description

2.1. Some simple examples

1. Convert an input media file to different format, by re-encoding media streams

   ffmpeg -i input.avi output.mp4

2. Set the vidio bitrate to 64 kb/s and a buffer size of 64 kb

   ffmpeg -i input.avi -b:v 64k -bufsize 64k output.mp4

3. Force the frame rate of the output file to 24 fps

   ffmpeg -i input.avi -r 24 output.mp4

4. Force the frame rate of the input file (valid for raw formats only) to 1 fps and the frame rate of the ouput file to 24 fps

   ffmpeg -r 1 -i input.avi -r 24 output.mp4

3. Detailed description

Transcoding process

3.1. Filtering

Before encoding, ffmpg can process raw audio and video frames using filters from the libavfilter library.

Simple filtergraphs

Simple filtergraphs are those that have excatly one input and output, both of the same type.

A simple filtergraph for video can look for example like this

Some filters change frame properties but not frame contents. E.g.

• the fps filter in the example above changes number of frames, but doesn't touch the frame contents
• the setpts filter, which only sets timestamps and otherwise passes the frames unchanged

Complex filtergraphs

Complexx filtergraphs are those which cannot be described as simply a linear processing chain applied to one stream. E.g.

• more than one input and/or output
• when output stream type is different from input

3.2. Steam copy

Steam copy is a mode selected by supplying the copy parameter to the -codec option.

It only demuxing and muxing, so it is very fast and there is no quality loss.

4. Stream selection

• -mapoption for manual control of stream selection in each output file

  ffmpeg -i input.mp4 -map 0:v:0 -map 0:a:0 ouput.mp4

• -vn skip video streams

  ffmpeg -i input.mp4 -vn output.mp4

• -an skip audio streams

  ffmpeg -i input.mp4 -an output.mp4

• -sn skip subtitle streams

  ffmpeg -i input.mp4 -sn output.mp4

• -dn skip data streams

  ffmpeg -i input.mp4 -dn output.mp4

4.1. Description

The sub-sections that follow describe the various rules that are involved in stream selection

Automatic stream selection

• for video, it is the stream with the highest resolution
• for audio, it is the stream with the most channels
• for subtitles, it is the first subtitle stream found but there's a caveat. The output format's default subtitle encoder can be either text-based or image-based, and only a subtitle stream of the same type will be chosen
• the stream with the lowest index is selected in advance
• data or attachment streams are not automatically selected and can only be included using -map

Manual steam selection

When -map is used, only user-mapped stream are included in that ouput file.

Complex filtergraphs

If there are any complex filtergraph output streams with unlabeled pads, they will be added to the first ouput file.

Stream handing

Steam handing is independent of stream selection.

Stream handing is set via the -codec option addressed to streams within a specific output file

4.2. Examples

The following examples illustreatethe behavior, quirks and limitations of ffmpeg's stream selection methods

Assume the following three input files

input file 'A.avi'
 stream 0: video 640x360
 stream 1: audio 2channels

input file 'B.mp4'
 stream 0: video 1920x1080
 stream 1: audio 2 channels
 stream 2: subtitles (text)
 stream 3: audio 5.1 channels
 stream 4: subtitles (text)

input file 'C.mkv'
 stream 0: video 1280x720
 stream 1: audio 2 channels
 stream 2: subtitles (image)

• .avi, .mkv, .mov, .mp4: support video, audio
• .wav: only support audio

Example: automatic stream selection

ffmpeg -i A.avi -i B.mp4 out1.mkv out2.wav -map 1:a -c:a copy out3.mov

• out1.mkv
  • video: select stream0 from B.mp4, whic has the hightest resolution
  • audio: select stream3 from B.mp4, since it has the greatest number of channels
  • subtitles: select stream2 from B.mp4, which is the first subtitle stream
• out2.wav
  • audio: select stream3 from B.mp4
• out3.mov
  • -map 1:a: select all audio streams from the second input B.mp4
  • -c:a copy: copy audio streams, so no decoding-filtering-encoding operations

Example: automatic subtitles selection

ffmpeg -i C.mkv out1.mkv -c:s dvdsub -an out2.mkv

• out1.mkv
  • the subtitle stream of C.mkv is image-based and the default subtilte encoder of the Matroska muxer is text-based, so subtitles stream will not be selected
  • only a video and audio stream shall be selected
• out2.mkv
  • a subtitle encoder is specified and so the subtitle stream is selected
  • in addtion to the video stream

Example: unlabeled filtergraph outputs

ffmpeg -i A.avi -i C.mkv -i B.mp4 -filter_complex "overlay" out1.mp4 out2.srt

• out1.mp4
  • -filter_complex "overlay": requires exactly two video inputs, but none are specified, so the first two video streams are used, those of A.avi adn C.mkv, automatic selection of the video stream is skipped
  • the audio stream shall automatically chose stream3 in B.mp4
  • no subtitle stream is chosen
• out2.srt
  • only accept text-based subtitle streams. So skip the image-based subtitle stream in C.mkv and choose stream 2 in B.mp4

Example: labeled filtergraph outputs

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5. Options

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5.1. Stream specifiers

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5.2. Generic options

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5.3. AVOptions

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5.4. Main options

-f format(input/output)

Force input or output file format.

The format is normally auto detected for input files and guessed from the file extension for output files, so this option is not needed in most cases

e.g. ffmpeg -i input.avi -f mp4 output.mp4

-i url(input)

Input file url

6. References

1. https://ffmpeg.org/ffmpeg.html