[vorbis-dev] Questions about window sizes

[Michael Smith]

On Thursday 06 March 2003 12:46, stoffke at directbox.com wrote:
> Hello,
> I have a few questions about the block size in ogg vorbis
> 1. The allowed blocksizes are powers of two between 64 and 8192 Samples.
> As I understood , there are  fixed sizes for long and short blocks .
> The encoder can pick any allowed value for long blocks and onother value,
> that must be smaller or equal to the first one, for short blocks.
> On which base does the encoder choose the size for long/short blocks ?
> Why are there so many possible blocksizes - would it be necessary
> to analyze the entire track to find the out, which sizes fits best ?

libvorbis 1.0 makes the decision based on target quality/bitrate. The 
different possibilities are there so that a given encoder can choose a 
variety of different strategies for different purposes.

>
> 2. How does the encoder decide , whether to use short or long blocks during
> encoding ? In earlier versions, it was done "by 4 parallel bandpass filters
> that detect energy surges", but Monty said it will be changed.
> (http://www.xiph.org/archives/vorbis-dev/200109/0054.html )
>

Not really sure what 1.0 does - have a look at lib/envelope.c, i think.

Mike

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