[vorbis-dev] Re: RT & codebooks [was streaming metadata requirements

Monty 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 beginning.

> 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
HTTP pushability.


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