[MPlayer-users] [Question] Why 2 channel ac3

[Ed Fisher]

On Thu, Dec 26, 2002 at 06:56:16AM +0100, Robert R. Wal spake thus:
> The reason for riping DVD-s with reencoding AC3->AC3 is that the moronic
> ``release groups'' think it makes them more cool, since almost all Windows
> users believes that AC3 means ``DVD quality''.
> 
> Which is far from the truth.
> 
> AC3 is ``old codec'' slightly better than mp3, but much worse than
> Vorbis, AAC or WMA (at the same bitrates). When you recompress 5.1 AC3
> streams you get artifacts from the lossy compression, mixed with
> additional artifacts from downmixing+normalising six tracks to two.
> 

http://www.atsc.org/standards/a_52a.pdf -- The official ac3 spec,
revised 20 august 2001.  Just for reference.

I think your assumption that release groups are using a 5.1ch ac3
reencoded to 2ch ac3 is *very* dubious.  No release group I know of
would EVER do that.  If there was no 2ch ac3, they would simply release
either the full 5.1ch or an mp3/vorbis reencode.  

Yes, ac3 is lossy, but your message sounds almost like you're advocating
people reencode 5.1ch ac3 to 2ch vorbis rather than use the 2ch ac3,
which is really very wrong.  And, in any case, the two standard formats
for any divx or xvid released are mp3 and ac3, and an ac3 downmixed by
the release group to 2ch would get nuked immediately.  

In other words: if there is a 2 channel ac3 track, and you can spare
192kbit/s, USE IT.  Only reencode if you absolutely have to.  No matter
what, unless you're using something like MLP, it's going to be lossy and
sound worse than the original stream.  

Anyway, your entire email seems to be based on the premise that release
groups are downmixing 5.1ch ac3 to 2ch ac3 themselves, and that's
definitely not true.

-gleam


-- 
The pollution's at that awkward stage.  Too thick to navigate and too
thin to cultivate.
		-- Doug Sneyd