[vorbis] Codebook Flexibility

[Gregory Maxwell]

On Sun, Dec 24, 2000 at 04:41:32PM +0200, Cherniavsky Beni wrote:
> A somewhat unrelated question: how different is the MP3 decoding from
> Vorbis?  Specifically, can we create a lossless mapping utility from
> MP3 to Vorbis without re-encoding (using a specialized for this codebook
> maybe - although MP3 doesn't use vq).

The blocking and MDCT are different, so no go. If the MDCT domain were the
same, it might be possible to losslessly recode the MDCT recode the MDCT
spectrum (i.e. I think that AC3 and MP3 might be the same), but it's likely
that the resultant vorbis file would be larger then the MP3 (the way
quantization is performed is sufficiently different that the quantization
noise would look like entropy to the vorbis encoder).

Furthermore, the *only* advantage to moving MP3->vorbis would be to avoid
patent problems (You're likely to get lower bitrates at anywhere near the
quality due to similar sorts of perceptual mismatch), but doing so would
not free you of the mp3 patents: Since a (patented) mp3 encoder would have
been integral to the creation of such files (even though the presence of
the mp3 encoder almost certainly reduced the quality of the end result),
additionally, the presence of the mp3 step in would almost certainly be
detectable.

It would likely be determined that such as file would be equally applicable to

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