The best way to understand -map option is to think of it like a way to tell FFmpeg which streams do you want to select/copy from input to output.
The order of -map options, specified on cmd line, will create the same order of streams in the output file.
Here are several examples.
Input file
In all following examples, we will use an example input file like this one:
# fmpeg -i input.mkv
ffmpeg version ... Copyright (c) 2000-2012 the FFmpeg developers
...
Input #0, matroska,webm, from 'input.mkv':
Duration: 01:39:44.02, start: 0.000000, bitrate: 5793 kb/s
Stream #0:0(eng): Video: h264 (High), yuv420p, 1920x800, 23.98 fps,
23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(ger): Audio: dts (DTS), 48000 Hz, 5.1(side), s16, 1536 kb/s (default)
Stream #0:2(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), s16, 1536 kb/s
Stream #0:3(ger): Subtitle: text (default)
At least one output file must be specified
#
Example 1
Now, let’s say we wan’t to:
- copy video stream
- encode german audio stream to mp3 (128kbps) and aac (96kbps) (creating 2 audio streams in the output)
- drop english audio stream
- copy subtitle stream
This can be done using the following FFmpeg command line:
ffmpeg -i input.mkv \
-map 0:0 -map 0:1 -map 0:1 -map 0:3 \
-c:v copy \
-c:a:0 libmp3lame -b:a:0 128k \
-c:a:1 libfaac -b:a:1 96k \
-c:s copy \
output.mkv
Note there is no “-map 0:2” and that “-map 0:1” has been specified twice.
Using “-map 0:0 -map 0:1 -map 0:1 -map 0:3” we told FFmpeg to select/map specified input streams to output in that order.
So, our output will now have the following streams:
Output #0, matroska, to 'output.mkv':
Stream #0:0(eng): Video ...
Stream #0:1(ger): Audio ...
Stream #0:2(ger): Audio ...
Stream #0:3(ger): Subtitle ...
After we selected which streams we would like in our output, using “-map” option, we specified codecs for each stream in our output.
Video and subtitle stream have just been copied and german audio stream has been encoded to 2 new audio streams, mp3 and aac.
We used “-c:a:0” to specify codec for the output’s first AUDIO stream and “-c:a:1” to specify codec for the output’s second AUDIO stream.
Note that “a:0” refers to the output’s first AUDIO stream (#0:1 in our case), “a:1” refers to the output’s 2nd AUDIO stream (#0:2 in our case), etc.
The result will be:
Output #0, matroska, to 'output.mkv':
Stream #0:0(eng): Video ...
Stream #0:1(ger): Audio ...
Stream #0:2(ger): Audio ...
Stream #0:3(ger): Subtitle ...
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (dca -> libmp3lame)
Stream #0:2 -> #0:2 (dca -> libfaac)
Stream #0:3 -> #0:3 (copy)
Example 2
Let’s say that we want to reorder input streams backwards, so that we have output like this:
Stream #0:0(ger): Subtitle: text (default)
Stream #0:1(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), s16, 1536 kb/s
Stream #0:2(ger): Audio: dts (DTS), 48000 Hz, 5.1(side), s16, 1536 kb/s (default)
Stream #0:3(eng): Video: h264 (High), yuv420p, 1920x800, 23.98 fps,
23.98 tbr, 1k tbn, 47.95 tbc (default)
This can simply be done using the following command line:
ffmpeg -i input.mkv -map 0:3 -map 0:2 -map 0:1 -map 0:0 -c copy output.mkv
Note that we specified all the input streams, but in the reverse order, which causes that order to be respected in the output.
The option “-c copy” tells FFmpeg to use “copy” on all streams.
Example 3
If we want to extract only audio streams, from input file, then we can do it like this:
ffmpeg -i input.mkv -map 0:1 -map 0:2 -c copy output.mkv
Example 4
If we want to re-encode just the video streams, but copy all the other streams (like audio, subtitles, attachments, etc), we might use something like this:
ffmpeg -i input.mkv -map 0 -c copy -c:v mpeg2video output.mkv
It will tell ffmpeg to:
- read the input file ‘input.mkv’
- select all the input streams (first input = 0) to be processed (using “-map 0”)
- mark all the streams to be just copied to the output (using “-c copy”)
- mark just the video streams to be re-encoded (using “-c:v mpeg2video”)
- write the output file ‘output.mkv’
Original Article Here