[FFmpeg-devel] Flac encoder and MPEG4 ALS

Baptiste Coudurier baptiste.coudurier
Sun Mar 30 16:00:33 CEST 2008


Justin Ruggles wrote:
> Benjamin Zores wrote:
>> Kostya a ?crit :
>>> On Sun, Mar 30, 2008 at 03:35:22PM +0000, 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.
>>> Just curious - is it possible now to distinguish ALS from ordinary AAC in mp4
>>> container without extra hack (i.e. looking into extradata)?  
>> Using audio-only, it can be contained in WAVE/AIFF/BWF container with 
>> 'A' 'L' 'S' 0x00 FourCC but I can't tell for MP4.
> I don't know a lot about MP4 yet.  The object type ID is 36....don't
> know if that makes it easy to distinguish.

I see, this is mpeg-4 audio object type, not mpeg-4 system object type,
which is still 0x40 for 14496-3.

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