[vorbis] bitpeeler

[Kyle Rose]

No offense, Segher, but the output quality of this thing is awful. =)

I'll disregard the fact that, at least with *my* compiler, the source
tarball I downloaded reduces every packet to zero bytes, which isn't
terribly interesting.

I decided to set the byte reduction to something constant: I started
by dividing each packet's size by 2 just to see what would happen.
The resulting ogg file was basically unlistenable.  Yes, it sounded
like the original music, but there were *terrible* artifacts
throughout the music, mostly sounding like constant-frequency tones
overlaying the music, each lasting for a short fraction of a second.
At 2/3 of the original bitrate, the artifacts were still almost as
bad.

By contrast, encoding the original wav file at 64 kbits produces a
much smaller file than either of these tries, and sounds significantly
better.

I'm starting to get the impression that (excuse me while I commit what
is probably an atrocity wrt to the Vorbis algorithm) the compression
used by Vorbis isn't a "stable" sequence, i.e., one for which

               |S_{n+1} - S_n| < 1/k |S_n - S_{n-1}|

otherwise, I suspect that cutting out half the bits would degrade the
sound quality significantly, but wouldn't introduce the kinds of
artifacts I was hearing.

A utility that needs to do some inexpensive analysis of the file (or
of each packet) to determine a nearly-optimal shorter sequence
representing the same waveform would be much preferred to a utility
like apr, which is essentially useless for any real-world application.

Of course, if the encoder could be altered to allow the use of a
utility as simple as apr to perform adequate bitpeeling, that would be
even better in the long run: but I'd still have my 10,000-strong
collection of Ogg's to re-rip, which would leave me terribly unhappy
at the misleading carrot-on-a-stick promotion of "bitpeeling" these
past two years.

Cheers,
Kyle
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