[vorbis] questions

[Segher Boessenkool]

"Mercier, Dave" wrote:
> 
> We haven't attempted to create an embedded version, but we did examine some
> of these issues when seeing if it could be used in video games. I'll state
> here that I didn't actually do the work, I'm just relaying the results of
> our research.
> 
> What we found was that the biggest problem was not the MIPS required
> (although that's always an issue too). The biggest problem was the memory
> footprint required. Apparently as of beta 2, it required about 1 megabyte of
> memory to perform decoding. We reduced that to about 500k by using shorts in
> the codebook expansion instead of ints. Of that 500k, about 250k could be

If the codebooks are maptype 1, you can save almost all of the memory required.
Just don't expand it, but only unpack when decoding vectors.

> may be overlooking some simple optimizations to the memory footprint. I know
> for our case (video games), we can't really afford that much memory use - it
> kind of defeats the purpose of the compression for us.

If you are in control of what streams will be played on it (i.e., you
encode the streams yourslef), you can leave everything out of the
decoder that isn't needed. If you need specific help, don't be afraid
to ask.

> So if your embedded device doesn't have much memory, and I think many don't
> have that much (I'm not an expert on them), it may be a problem getting

Most have 1M-4M nowadays.

> Vorbis implemented on them. I'm sure there are lots where it would fit
> though, and maybe there is a way to deal with looking through the code books
> on the fly instead of pre-decoding them.

Lattice books can be decoded on-the-fly; general books not.

Hope this helps,

Segher

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