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

[Wayde Milas]

On Wed, 2004-06-09 at 07:19, Alexei Khlebnikov wrote:

> As to the sound encoding, I agree that 96k is probably too little,
> but 112 or 128 kbps vorbis should be enough for movies without lot
> of music, for slightly-above-average home user. When music is the
> important part of the movie, e.g. in LOTR, I agree, 192kbps is needed.

192k vorbis on LoTR is useless too. (On a good 5.1 system) You are
throwing away 4 channels of information. Well, not throwing away, but
mixing them down to 2 channels and then throwing information away to
squeeze the 384k or whatever bitrate down to 192.

Here is the truth. 384k Ac3 5.1 is already compressed all to hell.
Seriously. This is what happens: They take a master of say 6 channels
(this isnt quite right because some of the channels arent full bitrate,
but its close enough to get a good idea) of 24 bit sound. The sampling
rate is usually 48khz. This is compared to CD which is 2 channels of 16
bit at 44.1khz.

Ok so you got 6*24*48000 = 6912000 bits per second. Now they take this
monster stream, and compress it down to 384k - 384*1024 = 393216. See
the huge amount thats already thrown out?

Yes they do some funky acoustical modeling and phase shifting so it
makes it really hard to detect the differences, and all the channels
arent active all at once most times so alot of of the bits that tossed
are not meaningless. The point here is that the 5.1 audio stream is
already HEAVILY compressed.

To take this alread compressed stream, extract it back out to 5.1,
downmix it to 2 channel, then sample it down to 192, or god fobid, 96k
is asking for trouble. You are going to end up with a stream that sounds
like garbage on a 5.1 system compared to the 5.1 ac3 stream on said
system.

HOWEVER, if you are playing that 196k stream on a cheapy 2 speaker
powered audion system hooked directly to your computer, you might not be
able to tell the difference, because teh original ac3 5.1 stream would
have to be downmixed and resampled to start with to get it to play
correctly on just 2 speakers.

Its all a function of what equipment you have, and how you are listening
to the stream.
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