[CELT-dev] Variable frame size and API changes

[Jean-Marc Valin]

Hi Pascal,

I think you would get much better performance if you were to pack multiple CELT
frames together inside your "DAB frames". For example, you could easily do 24
ms at 48 kHz by concatenating 2 frames of 12 ms (576 samples) or 3 frames of 8
ms (384 samples). There's nothing that forces you to have one CELT frame per
DAB frame.

Cheers,

    Jean-Marc

Quoting Pascal Charest <c.lacsap at gmail.com>:

> Hi Jean-Marc,
>
> If celtenc framesize parameter is the number of samples per frame, I
> can get 24 ms frame with 32kHz, 24kHz and 16kHz source. It is not
> possible with 48kHz input as only 64 to 1024 framesize are supported.
>
> For example, to obtain a 24ms framesize, I can use a 32kHz input with
> the following command:
> celtenc --framesize 768 input-32kHz.wav output.oga
>
> I've tested the previous command it with celt version 0.7.1 and 0.6.1
> and had no problem encoding and decoding.
>
> For CELT over DAB, CELT can be configured to use 48, 32, 24 and 16 kHz
> source. The allowed CELT framesize is 24, 12, 8 and 6 ms. Any mix of
> these parameters can be used, except for 48 kHz / 24 ms that is not
> supported by the CELT codec code. Once the channel is configured, we
> don't plan to change its parameters real-time.
>
> Pascal
>
>
> 2010/5/19 Jean-Marc Valin <Jean-Marc.Valin at usherbrooke.ca>:
> > Hi Pascal,
> >
> > My question is what *CELT* frame size you are using in your protocol? CELT
> does
> > not currently support 24 ms frames, so I assume you are using smaller
> frames,
> > right? What size are they?
> >
> > Thanks,
> >
> >  Jean-Marc
> >
> > Quoting Pascal Charest <c.lacsap at gmail.com>:
> >
> >> Hi Jean-Marc,
> >>
> >> The current CELT over DAB framing allows to user to select between 24,
> >> 12, 8 and 6 ms frame size. Although it is not necessary, it would be
> >> easy to add support for 4, 3, 2 and 1 ms.
> >>
> >> By the way, it was really easy to create a protocol for CELT over DAB
> >> because this codec offers great choices for the frame size and
> >> bitrate. Moreover, the availability of CBR was the most useful
> >> property because the underlying channel is constant bitrate.
> >>
> >> Pascal
> >>
> >> 2010/5/18 Jean-Marc Valin <Jean-Marc.Valin at usherbrooke.ca>:
> >> > Hi,
> >> >
> >> > What frame size are you using to get 24 ms "chunks"? I assume that's not
> >> 9*2.5
> >> > ms, right?
> >> >
> >> >   Jean-Marc
> >> >
> >> > Quoting Pascal Charest <c.lacsap at gmail.com>:
> >> >
> >> >> Hi Jean-Marc,
> >> >>
> >> >> DAB frame size is based on MPEG1/2 audio, which is 24ms. As such, any
> >> >> 24ms compatible frame size would keep the CELT over DAB framing easier
>
>