[MPlayer-users] RFC: docs update for "how to create a high quality DVD rip"

[Wayde Milas]

On Wed, 2004-06-09 at 14:24, Wayde Milas wrote:
> On Wed, 2004-06-09 at 12:53, rcooley wrote:
> > On Wed, 09 Jun 2004 11:09:35 -0400
> > Jason Tackaberry <tack at sault.org> wrote:
> > 
> > > but just because you don't have an A/V receiver for AC3
> > >         pass-through today doesn't mean you won't have one tomorrow.
> > 
> > Or, you could encode it to multi-channel Vorbis.  I'd say any reciever
> > that can do 5.1 AC3 pass-through should be able to handle
> > uncompressed 6-channel input.
> 
> Yea, how though?
> 
> I can't seem to find a multichannel vorbis encoder that works, plus you
> got the physical transport.. multichannel vorbis means you are going to
> have to use analog outs... I think. To get it down a spdif pipe you are
> going to want to use ac3 because the other end (your reciever) generally
> only understands 2 channel spdif and ac3 5.1 or 5.2 or whatever. Feeding
> it 3 or 4 or 5 channels independantly will jsut confuse it.
> 
> So you need to rencode it to ac3 5.1 on the fly. although there are libs
> to do this, I know of no code that ties it all together.

I played around with this. I used extract_a52 to rip the ac3 stream
(448k in this case) to a file. then used a52decode to decode the ac3
stream to a 6 channel pcm file.

Used vorbis to encode this 6 channel pcm stream to a 6 channel vorbis
stream.

Worked fine. Problem is that unless you sue a really low quality, the
vorbis stream will be llarger than teh ac3 stream. quality 3 makes the
vorbis stream 375k. Of course, quality 3 sounds like hell (to me).

quality 7 (sounds good to me) results in a much bigger stream than teh
original.

As someone mentioned before, vorbis currently has very poor modeling on
stream larger than 2 channels.

If this gets fixed in the future, encoding a 6 channel vorbis stream
should be a viable option.

For fun I tried using flac to encode the 6 channel pcm. (Yes I know,
silly but i wanted to see how flac handled it). Flac should handle more
than 2 channels with --channels. It puked (couldnt unerstand the fmt
subblock).
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