Re: [AVT] Requesting feedback on new CELT codec

["Gregory Maxwell" <gmaxwell at gmail.com>]

Steve Underwood <steveu at coppice.org> wrote:
> So far Polycom has managed to get each of its codecs into an ITU spec - G.722.1, G.722.1C and G.719. However, I've only ever seen
> these things supported by Polycom products. That is in spite of the patents on G.722.1C being offered royalty free. An ITU spec is no
> guarantee of anything happening in the real world.
[snip]

This may be because G.722.1C 'royalty free license' has a fairly
gnarly patent termination clause that might make it a 'costly'
proposition for commercial players, and the license also includes
advertising requirements and sub-licensing prohibitions which make it
incompatible with free software licensing.  ... it also may be just
because the performance is somewhat lack-luster: It offers fairly high
latency yet faired pretty poorly in our listening tests.
(http://www.celt-codec.org/comparison/) OTOH, G.722.1C is
computationally cheap...

Swinging this back on topic a bit more:   With typical frame sizes in
the range of 8ms any overhead is very harmful.  CELT does a fairly
good job of avoiding overhead internally, not wasting more than ~1 bit
or so per frame.

But this means that the codec's several tunables are not signaled in
the individual frames:  Sample rate, frame size, and stereo/mono must
be explicitly and correctly negotiated out of band or the codec will
fail to decode. (Bitrate need not be signaled: the codec can infer the
bitrate from the frame sizes).   So it's important for CELT today that
some higher level system takes care of working out these details.  Is
this a requirement which would harm some applications?
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