Mix down 5.1 AC3 to Stereo WAV?

Question

I wonder if I can mix down a 5.1 AC3 file to Stereo WAV file, i.e. 6-channel > 2-channel. I'd like to know how to do this with via terminal with ffmpeg (or avconv, because it says ffmpeg is deprecated).

Answer 1

From man avconv, Audio Options section:

-ac[:stream_specifier] channels (input/output,per-stream)
           Set the number of audio channels. For output streams it is set by
           default to the number of input audio channels. For input streams
           this option only makes sense for audio grabbing devices and raw
           demuxers and is mapped to the corresponding demuxer options.

So you basic command line would be:

avconv -i <input file> -ac 2 <output file>.wav

You may also play with downmixing settings for the AC3 decoder, ie, the options where you can configure how the 6 channels from 5.1 will be merged (downmixed) into the 2 of stereo. Check for -dmix_mode and the -*mixlev* family of options under the Audio Encoders / ac3 section of the manual

Answer 2

I don't know if avconv supports Dolby Pro Logic II, but ffmpeg does. I use the following command:

IFL=input.ac3
OFL=output.ogg
/usr/bin/ffmpeg -i "$IFL" \
   -codec:a libvorbis -qscale:a 6 \
   -ac 2 -af "aresample=matrix_encoding=dplii" \
   "$OFL"

The question was for WAV. See ffmpeg documentation for how to use wavpack instead of libvorbis.