[vorbis-dev] Re: RT & codebooks [was streaming metadata requirements
xiphmont at xiph.org
Wed Jun 13 13:21:03 PDT 2001
> In practice, many vorbis files will be using standard codebooks. In
> previous posts, you have said that optimising codebooks for a file
> give a maybe 1% advantage.
This is true enough *right now*. Note that every mode has different
books however. Having all the currently used codebooks in each
decoder app would be about 4MB of static data.
> It makes no sense to add this much overhead to a stream, and it will
> prevent anyone joining a stream in the middle if the have to wait for
> codebooks to come by.
Not correct! When someone connects, the server pushes out a header
then starts streaming. You do *not* need to start from the beginning
of a stream! You only need the header, and it can just be tacked onto
> The way JPEG coped with a very similar problem in RTP (sending the
> quantization and Huffman tables) was to set aside a byte in each
> packet to define which one is being used. They then defined 0-127 to
> be predefined ones, and 128-255 to be dynamic ones, and added a way
> to specify the dynamic ones inline at regular intervals.
Every beta has used different codebooks, about a half a meg worth.
This will naturally stabilize (at least in *our* encoder) after a
time, but the variability of codebooks is one of the big reasons we
have such a quality edge over mp3, and not something to simply be
discarded because it's a harder technical problem than mp3's trivial
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