ffmpeg: isolate one audio channel

How can I use ffmpeg to isolate one channel from an audio file? I have a stereo audio file, and I need the output to be the contents of the right channel in a mono audio file.

While I'm sure it's fairly easy to do, I can't figure it out. Thanks for the help!

Answer

You have two methods:

The pan audio filter is powerful but the syntax takes some time to understand.

It is helpful to refer to the channel layouts list when using pan: ffmpeg -layouts

Stereo right channel to mono:

ffmpeg -i stereo.wav -af pan=mono|FC=FR right_mono.wav

...which is the same as:

ffmpeg -i stereo.wav -af pan=1|c0=c1 right_mono.wav

• mono is output channel layout or number of channels. Alternatively you could use 1 instead of mono.


• FC=FR create the Front Center channel of the output from the Front Right of the input.


• c0=c1 is the same as the above in this case: create the first (and only) channel of the mono output (c0) from the second channel (c1) of the input.


• If you want the left channel instead use FC=FL or c0=c0.

See the pan audio filter documentation for more info.

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You can use the -map_channel option. It uses pan in the background and is somewhat less flexible.

ffmpeg -i stereo.wav -map_channel 0.0.1 right_mono.wav

• The first 0 is the input file id


• The next 0 is the stream specifier


• The 1 is the channel id

So this can be translated as: first file, first stream, second channel (or right channel).

From the -map_channel documentation:

The order of the -map_channel option specifies the order of the channels in the output stream. The output channel layout is guessed from the number of channels mapped (mono if one -map_channel, stereo if two, etc.