[FFmpeg-devel] [PATCH] als in mp4

Robert Swain robert.swain
Mon Mar 23 17:08:50 CET 2009

On 23/3/09 06:40, Alex Converse wrote:
> On Mon, Mar 23, 2009 at 2:29 AM, Baptiste Coudurier
> <baptiste.coudurier at gmail.com>  wrote:
>> Jai Menon wrote:
>>> On 3/23/09, Baptiste Coudurier<baptiste.coudurier at gmail.com>  wrote:
>>>> Jai Menon wrote:
>>>>   >>  [...]
>>>>   >>
>>>>   >>  When were they initially set to the correct values?
>>>>   >
>>>>   >  stsd atom/box? i think
>>>>   >
>>>> Hummm, stsd does not contain the correct sample number for everything
>>>>   using 'mp4a' tag. Values are correct in 'esds' box.
>>> Which means we should parse the extradata (in this case als specific
>>> conf) and get values from there? I can do this for als by maybe adding
>>> a new function to mpeg4audio.c.
>> I don't know how exactly ALS works, but it might use the
>> AudioSpecificConfig like others, this code might belong to mpeg4audio.c,
>> yes.
> It's set in the AOTSpecificConfig. In this case it is the
> ALSSpecificConfig for AAC it is the GASpecificConfig. Both of these
> are embedded in the AudioSpecificConfig.
> Right now for AAC we just leave it set to zero and the decoder figures
> it out just fine.
> Rob: care to weigh in?

It would make sense to me to parse the AOTSpecificConfigs in 
mpeg4audio.c. This should allow all useful general information about the 
streams to be available before decoding - right?

For the moment it is acceptable, in my opinion, to commit whatever would 
be consistent and leave markers stating lack of support for stream copy 
or so. In the long term, supporting parsing and rewriting of the 
specific configs is probably the way to go.

Any comments? :)


More information about the ffmpeg-devel mailing list