[FFmpeg-devel] Flac encoder and MPEG4 ALS

[Justin Ruggles]

Kostya wrote:
> On Sun, Mar 30, 2008 at 08:34:18AM -0400, Justin Ruggles wrote:
>> Jai Menon wrote:
>>> On Sunday 30 March 2008 08:48:52 Benjamin Zores wrote:
>>>> Jai Menon a ?crit :
>>>>> Hi,
>>>>>
>>>>> I started some basic work on the MPEG4 ALS encoder and I get the feeling
>>>>> that I could reuse a lot of code from the flac encoder. So
>>>>> (hypothetically ;-)) if I were to submit a patch, is it okay if I move
>>>>> some code out of flacenc.c to a shared source file?
>>>> IIRC we don't even have a decoder for that atm.
>>>> Do you have a working ffmpeg decoder for that or are you using the
>>>> closed mp4alsRM19 binary ?
>>> Very correct. It would be more sensible to write a decoder for  libavcodec 
>>> before pursuing this. But this "work" on the encoder is with reference to the 
>>> GSoC task. I'm using the RM20 reference decoder and it suits my current 
>>> purpose. Also i think that the encoder would be tested/verified against the 
>>> reference.
>> A decoder, in this case, is a much larger task since ALS has several
>> different optional extensions that would have to be supported.  If you
>> feel that you are up to the task, by all means submit a proposal.  I
>> chose to suggest an encoder because it is more flexible as far as the
>> timeframe, and therefore much more likely to make it to SVN by the end
>> of the summer.
> 
> I've looked at it once. Seems the most features are for floating-point
> mode, baseline decoder should be comparatively easy. Especially if you
> are the person who writes encoder to it ;)

It has 2 entropy coders, plus another for floating-point.  It has 2 ways
of doing multi-channel.  There are also several prediction methods.  The
spec does not specifically say what is "baseline" vs. extended, but it
would be simple enough to break down the task.

> Too bad the spec costs money and available drafts allow you to write
> some hybrid between LPAC and ALS. At least we have the reference
> decoder and encoder sources.

I have paid for the spec.  If this becomes an SoC project, I will share
it only with the student.  I won't make it publicly available though.

-Justin