[vorbis] bitpeeler

[Graham Mitchell]

> >Yes.  But libvorbis-1.0 encoded streams are not very nicely peelable --
> >that's why I losslessly reencode them, first.
>
> Am I correct in guessing that you are referring to re-huff'ing them?

Both are lossless processes, but I don't think they are the same.  Rehuffing 
refers to replacing the generic huffman trees used for a given file with an 
optimal which is specific to that file.  This ends up reducing the file size 
a few percent, but doesn't provide any hinting for peelers.

The reason the optimal huffman trees aren't used by default is because doing 
so requires the ability to scan through the entirety of the data stream 
before starting encoding.  This would make it impossible to encode 
on-the-fly, which is a major goal for vorbis.

The reason hinting for peelers isn't done yet is because a) it's hard, b) up 
until recently it hasn't been anywhere near the front of the priority queue, 
and c) no one wants it bad enough to pay for development, so other things are 
being done first.

Optimal huffman codes will never be used by default, though there's been talk 
of adding an option to oggenc to enable a pre-encoding pass over the data to 
create them if you've got it all in advance.  Not sure if this is really 
planned anytime soon, but it's been mentioned.

Peeler hinting will eventually be done, but since it may be more 
computationally-intensive than just "normal" encoding it may not be the 
default.


-- 
Graham Mitchell - computer science teacher, Leander High School
"It is not possible to be 'incidentally a Christian'. The fact of
Christianity must be overwhelmingly first or nothing. This suggests a reason
for the dislike of Christians by nominal or non-Christians: their lives
contain no overwhelming firsts but many balances."
	-- Sheldon Vanauken

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