[MPlayer-users] Re: Again on 5.1 vorbis encoding

[Alessio Sangalli]

Rémi Guyomarch wrote:

> >(as many nowadays do, I have such an audio device integrated on the
> >motherboard) there should be no problems. Even in the cased you only
> >have stero speakers Mplayer should be able to downmix the 5.1 vorbis
> >audio (am I correct?).
>
>
> It does. Life isn't beautiful ? :)

Yes. A friend of mine had to write a direct show thing to be able to do 
something like this on a windows machine... ehehh


> >Now what I ask is: understanding all the problems and limits of this
> >approach, how can I extract the 5.1 audio from a DVD title and encode it
> >into a vorbis file?
>
>
> You must be aware that AFAIK channel coupling is only for stereo
> mode. The Vorbis encoder doesn't know anything about 5.1, this means
> even if you can encode 6 channels into an Vorbis stream, this won't
> get you much and will probably be way less efficient than with AC3.

I understand - and I've also read that such an improvement could be 
added to vorbis, but now the author is concerned with ogg own *video* 
codec. However, I want to use vorbis quality at 6, which already keeps 
separated audio tracks even for stereo data.

mmhh... I must check the ac3 dump size against a good-quality (6) 
encoded vorbis file. Perhaps you're right and it's not worth the 
conversion; I think however the vorbis file size will be quite smaller 
than the ac3 version.


> And now there's also the problem of channel mapping : who will decide
> which Vorbis channel will go where ?

Who knows? heheeh I only hope that as I decode from ac3 and encode to 
vorbis, the same mapping will be preserved when decoding vorbis to the 
actual pcm data for the soundcard...

> That said, if you want to experiment, try something like that :
>
> rm -f audiodump.pcm ; mkfifo -m 600 audiodump.pcm
> mplayer -quiet -vc null -vo null -channels 6 -noframedrop -aid 128 -ao 
> pcm -nowaveheader $1 &
> oggenc --raw --raw-bits=16 --raw-chan=6 --raw-rate=48000 -q 2 -o 
> audio6-en.ogg audiodump.pcm &
> wait
>
> mplayer -quiet -vc null -vo null -channels 2 -noframedrop -aid 129 -ao 
> pcm -nowaveheader $1 &
> oggenc --raw --raw-bits=16 --raw-chan=2 --raw-rate=48000 -q 1 -o 
> audio2-it.ogg audiodump.pcm &
> wait
> rm -f audiodump.pcm

I've got the idea. I'll try to encode in separate steps so I can compare 
the file sizes of the ac3, pcm, vorbis data in 5.1 and stereo modes.


> >streams all together? (sometimes the english sound track is 5.1 and the
> >italian one is only stereo)
>
>
> Why not ? ;)


I've heard of potential problems about this, but I'm glad it's not like 
this.


bye and thank you!!!
as