[MEncoder-users] Separating each of the 6 channels of ac3 file into separate wav files

[L Lee]

I recently originated a thread about multiplexing, but now I have a related
question about DVD audio.

I have developed a method to use MEncoder to transcode some HD h.264 files
to mpeg2. The picture looks really good and the audio sync is close, just
not quite close enough (for every 2 hours of video, the video component
comes out about a second shorter than the audio).

I can increase the tempo of the audio file just enough that it correctly
syncs with the video by incorporating a process to demux, convert the audio,
a 6 channel (dolby 5.1) ac3 file, into a stereo wav file using a52dec,
change the tempo using SoX (the most recent version of which is quite
robust), convert back to ac3 with ffmpeg, then re-mux.

The problem is that the method I just described gives me a stereo mix-down
of the audio when it is converted to wav, which is fine for most of the old
video I routinely convert, but now I have some stuff that's newer and I'd
like to preserve the 6 channels through the tempo change process.

I'm looking for the simplest possible way to separate those 6 channels into
discrete files, perform the tempo change on each and then combine them again
into a single ac3 file containing all 6 channels.

Can MPlayer's dumpaudio option or any other functions of MPlayer and
MEncoder perform any of the conversion parts of the operation?

I tried using the pan option, then dumpaudio, but the command I used
resulted in a file that still contained all the channels, so it's clear that
I don't understand the processing steps I'm trying to use:

mplayer -channels 1 -af pan=1:1:0:0:0:0:0 channel 0 audio.ac3 -dumpaudio
-dumpfile 1-channel.ac3

Help will be appreciated. Thanks very much!

-- 
Laine Lee