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

[belcampo]

socke wrote:
> belcampo schrieb:
>> socke wrote:
>>> 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"
>>>
>>>
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>>> MEncoder-users at mplayerhq.hu
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>> Whit what version of ffmpeg and sox does this work ? I tried several,
>> but get errors like:
>> Unknown input or output format: sox
>> sox FAIL formats: can't open input  `-': premature EOF
>> pipe:: Unknown format
> I use...
> FFmpeg version SVN-r19742 (I built it some day this month)
> SoX v14.3.0
> 
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That did it, Thanks a lot. I can now watch the news at 1.4 speed, also 
have a version for 'slowbrains' at 0.7 :-)