[CELT-dev] Variable frame size and API changes

[Pascal Charest]

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