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

[socke]

L Lee schrieb:
> 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!
>
>   
I recently did some ac3 speed change (for conversion between 24000/1001
and 25 fps). I used the following pipe to do so:

ffmpeg -v 0 -i "$AUDIOFILE" -f sox - \
| sox -S -V -p -p speed 1.04270833333333 \
| ffmpeg -v 0 -i - -acodec ac3 -ab 448000 -y "$AUDIOFILE2"