[Speex-dev] CELT 0.5.0 is out
jean-marc.valin at usherbrooke.ca
Thu Oct 16 04:21:23 PDT 2008
Aymeric Moizard a écrit :
>> None of that is defined yet, though I'm open to suggestions on how to do
>> the mapping.
> CELT/44100 and CELT/48000
> a=fmtp:105 stereo=on
> probably a latency value?
It would definitely need a frame_size value
> "CELT" doesn't seems to be used for any other existing audio related
> stuff? right?
Not yet. It's very new (bit-stream not frozen yet), so at this point,
there are a few early adopters, but that's it.
> I didn't read fully the doc...
> One question for you Jean-Marc: can you confirm that the decoder
> will receive enough information to autoconfigure itself when receiving
> RTP streams? One documentation sentence seems to not go in that
> direction while it's a requirement for VoIP and mainly for SIP
No. Unlike Speex, CELT will not be able to decode anything with no prior
information on the stream. To decode a stream of packets, CELT needs the
1) Sampling rate. It's not just for setting the soundcard's rate, if you
use the wrong rate, you get garbage.
3) Frame size in samples
4) If there's more than one frame in a packet, you need to tell it where
the boundary is. However, once that's done, CELT knows the bit-rate used
just from the packet size, so there's no need to signal a fixed
The main reason CELT can't do like Speex (I wish it could) is that in
Speex, the overhead of transmitting the mode info is 5 bits for
narrowband and 9 bits for wideband. With 10 ms frames, that's just 250
and 450 bps. With CELT, there would be a bit more data needed and the
frame size can be as small as 2 ms, so we could end up with several kbps
of mode signalling. In the current code, there's no signalling at all.
The good thing is that after a few frames, the decoder should at least
realise it's decoding garbage.
>>> Jean-Marc Valin wrote:
>>>> Hi everyone,
>>>> I'm happy to announce CELT version 0.5.0. This release includes
>>>> simplifications to the bit allocation code and includes a new
>>>> low-complexity mode that can be enabled (without breaking
>>>> on the encoder side. There are several other optimisations and bug
>>>> included. The API has also been slightly modified, so code using CELT
>>>> will have to be updated (only minor changes required).
>>>> You can download it from the website: http://www.celt-codec.org/
>>>> Please note that the bit-stream still isn't frozen which means that 1)
>>>> we can still improve things and 2) you can't rely on compatibility yet.
>>>> Speex-dev mailing list
>>>> Speex-dev at xiph.org
>> Speex-dev mailing list
>> Speex-dev at xiph.org
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