[Vorbis] Clarification on code books usage.

[sameen eajaz]

Dear All,

As i have understood it , the Huffman codebook uses a huffman code
present in the bitstream ( lets us say it is decoding a floor 1 Y value
using the specifed codebook number ) to walk through the  huffman code
book tree till it hits a leaf node which is nothing but the entry number.
If we consider our floor 1 Y value example , this entry number is
directly being used as the Y value. Here is an extract from the tremor
code for the same
"if((fit_value[j+k]=vorbis_book_decode(books+book,&vd->opb))==-1)" where
vorbis_book_decode is returning an entry number. If this is correct the
code books constructed for decoding of the floor at the encoder should
have as many entries as the maximum value of the floor 1 Y value can take
(seems to be 256 ) .

In the case of the residue computation the packed entry value decoded is
used to generate a residue vecotor ( whose length is equal to the code
book dimension ). In this case the number of entries could be more than
this . Are these assumptions correct Can someone throw more light on this
aspect ?

A related question. Is there a limit on the maximum code book entries
that could be present in a code book . What does this depend on ? So i
have seen a codebook with the maximum number of entries being 6536 (
being used for residue decode i hope ) for the "highnoon1a.ogg" file.

warm regards,

Sameen

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