= Introduction =

The best way to understand [http://ffmpeg.org/ffmpeg.html#Advanced-options -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'