[FFmpeg-devel] [PATCh] aac parser: Don't write channels, sample rate, and frame size each frame

[Alex Converse]

On Tue, Mar 2, 2010 at 5:03 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Mon, Mar 01, 2010 at 08:31:42PM -0500, Alex Converse wrote:
>> On Mon, Mar 1, 2010 at 8:23 PM, Michael Niedermayer <michaelni at gmx.at>wrote:
>>
>> > On Mon, Mar 01, 2010 at 08:16:48PM -0500, Alex Converse wrote:
>> > > They are part of the invariant header and shouldn't change each frame
>> > > anyway. This prevents them from overwriting information provided by
>> > > backwards compatible extensions.
>> >
>> > what you attached does not match the description
>> >
>> > besides "shouldn't change" gives me a strange feeling ...
>> > if we can support it changing it would be a nice "wish/feature request"
>> >
>>
>> According to the AAC specification they changing these vales from frame to
>> frame is forbidden. They are part of the fixed header.
>
> these are written in every spec, it seems not to stop the broadcast crowd
> from switching channels and such between programs/commercials/...
>
> Also if ffmpeg doesnt support X and another application does support X
> people switch applications instead of reporting bugs. (path of least
> work ...).

I've found several times that people report bugs for things X does
that FFmpeg does not. People complained that the sample rate and
channel count of pure LC streams was wrong because we didn't match
libfaad2.

> Do other players support changing samplerate/channels in aac?
>

I have no idea if other players support changing frequency, channel
count, or frame size midstream. Even if we wanted to support it the
decoder still gets the full ADTS headers. Just blindly spitting out
values from the parser into the codec context every frame doesn't seem
like the proper solution here.