[Vorbis-dev] Reg. vorbis for real-time audio
dholth at fastmail.fm
Fri Aug 26 12:09:48 PDT 2005
Shashank Khanvilkar wrote:
> From the vorbis decoder specification, it is clear that the decoder
> needs to have all the codebooks before decoding can actually begin.
> I will appreciate if someone can clear the following questions:
> 1. I guess the codebooks are derived from the actual input data.
> Probably the encoder may be making two passes through the input. The
> first pass finds out the frequency of different symbols and the second
> pass just replaces these symbols with the codewords.
> If the above is true:
> I wonder how vorbis encoder can be used for real-time data? Will it
> use some known codebooks or will it use someform of adaptive coding?
> Any help appreciated.
Last I checked oggenc does not try to invent a codebook from the source
audio but picks its codebook depending on the level of compression
that's desired. So two files encoded with oggenc -q3 will have the same
codebook. This is distinct from the huffman coding that's applied to the
Clever people then try to invent better sounding codebooks.
- Daniel Holth
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