[vorbis] Bit Rate Peeling Quality
larry at towanda.com
Mon Jun 23 19:40:41 PDT 2003
I would hope that the "q" levels for the peeler are defined so that
the quality of a vorbis stream peeled from q6 to q2 (for example) would
match the quality of a wav encoded at q2. Of course, the peeled file
might be bigger than the file encoded with the same "q" level, but the
(albeit subjective) sound quality should be the same.
I would also hope that the same kind of bitrate ceiling could be applied
to both the peeler and the encoder instead of specifying quality.
This would help for streaming.
> However, Segher claims (and I believe him) that it's possible to losslessly
> re-encode a v1 vorbis stream in such a way to make a peeler's job much
> easier. That is (to quote my man Bill Nye), "consider the following":
> a.wav --> b.ogg (at q6) --> [MAGIC] --> c.ogg (also q6) --> d.wav
> a.wav --> b.ogg (at q6) -------------------------------------> e.wav
> Okay, the important thing is that d.wav and e.wav are bit-for-bit identical.
> Thus the [MAGIC] phase is "lossless". The other important thing is that
> c.ogg is easily peeled, even though b.ogg is not. So c.ogg could be peeled
> down to q2, and the resulting ogg would sound a lot closer to a "pure" q2
> vorbis file directly from a.wav than would attempting to peel b.ogg.
> Finally, I'm pretty sure b.ogg and c.ogg would be identical in size, as well.
> Graham Mitchell - computer science teacher, Leander High School
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