[vorbis-dev] Transient coding: AAC vs. Vorbis

[Segher Boessenkool]

> Steven is talking about Vorbis, Segher.
> Vorbis makes use of the MDCT.

Vorbis makes use of any transform you want.  Currently there's
only one transform defined, and that's the MDCT, sure.  That
doesn't mean we're stuck with it forever.

Same goes for window shapes, btw.

> Obviously Vorbis I is wasting space in this example by
> coding 5 floor curves (G-K) that are very similar.
> AAC *shares* the scalefactor set B with these 5 windows
> thus saving space.

Sharing the floors decreases the space needed for the
floors, but increases the space needed for the
residues.  So this is a tradeoff.  Also, deciding
per group of packets if floors should be shared again
wastes a few bits; more tradeoffs.

I'm not saying what Vorbis currently does is optimal,
of course; just that this is not a silver bullet.

> It maybe also worth the effort to encode the channel's
> residue vectors as one big vector (per channel) by
> interleaving. I think this will also improve coding
> efficiency a bit.

Same comment.


Segher