[vorbis] bitrtate peeling and lossless compression

[Larry Fenske]

--- ndrw mchl grnbrg <amg at bewley.net> wrote:
> Nathan Johnson <johnsonn at agcs.com> wrote:
> : So, neither Vorbis nor Squish can encode losslessly and peel the bit-rate
> back
> : to lossy encoding.
> : Would it be practical to make an encoding scheme that would be capable of
> this?
> 
> Well, considering that lossless encoding needs to use completely different
> methods of compression than lossy encoding uses, the compressed file would
> almost *have* to be the size of the lossless encoded file + the lossy
> encoded file together, which would probably be as large as the original
> pcm file if not larger.

I don't know whether lossless and lossy need to use completely different
methods or not (I haven't looked at methods for either), but even if they did,
the resulting file would usually still be smaller.  Consider a 44,100
sample/second, 2 channel, 16 bit/sample/channel file.  That's about 1411Kb/s. 
FLAC (in my experience) produces a file between about 40-55% original size. 
Let's say 50%.  The maximum bitrate I remember seeing in vorbis is 350Kb/s.  So
1411Kb/s*50% + 350Kb/s is about 3/4 the size of the original.  

Granted, that's not a great size, but even if it did expand the pcm file, if it
would play back the original bits, and I could peel it (perhaps initially
removing the lossless part) to lower bitrates, that would satisfy my wants.  Of
course, the smaller the compressed file, the better.

Larry Fenske

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