[vorbis-dev] Vorbis packet sizes

[Michael Smith]

On Friday 06 June 2003 00:31, David Etherton wrote:
> > It would be good, in my opinion, to actually place some more constraints
>
> in
>
> > the spec. It's hard to advertise "Supports Ogg Vorbis 1.0" when you know
> > that's not true in all cases. What you actually meant is "Supports OggEnc
> > 1.0 files, and YMMV".
>
> I've been meaning to ask this for a while -- is there a way to pass
> particular parameters to oggenc to guarantee that the maximum memory
> required to decode a stream is bounded?  In particular, I'd be willing to
> give up some compression if it kept the codebooks smaller.  I'm looking to
> support ogg on gaming consoles where I have total control over the exact
> content I'm going to play.

The memory usage required for decoding the output of a particular version of 
libvorbis is predictable - all the modes use roughly similarly sized 
codebooks. So, given that you'll presumably be doing all your encoding with 
libvorbis 1.0-based encoders (or cvs, which in this respect is identical), 
your memory usage will be bounded.

>
> For that matter, is there a way to encode a stream in such a way that it
> will consume less CPU time to play back (probably at the expense of some
> compression).  Thinking about it a little bit, at least part of the decode
> process time must linear in the output sample rate, so I'm thinking of
> doing voiceovers or walla at 24Khz or even possibly 16Khz.  I'm hoping I
> can do music (stereo), walla (stereo), and voiceover (mono) all at the same
> time for less than the cost of two full 48Khz stereo streams.

Right - sample rate and number of channels are the main ones. Other than that, 
you'd really have to tweak the encoder internals, and I doubt it'd be worth 
it.

Lower bitrates should also take less cpu to decompress, simply because there 
are fewer codebook symbols to look up. I don't know that this is 
significant/noticable, though.

Mike

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