[FFmpeg-devel] who should set framesize?

Alex Converse alex.converse
Thu Jun 25 16:11:52 CEST 2009

On Thu, Jun 25, 2009 at 5:08 AM, Frank Barchard<fbarchard at google.com> wrote:
> On Thu, Jun 25, 2009 at 12:11 AM, Luca Abeni <lucabe72 at email.it> wrote:
>> Ronald S. Bultje wrote:
>>> Hi Luca,
>>> On Wed, Jun 24, 2009 at 10:55 AM, Luca Abeni <lucabe72 at email.it> wrote:
>>> ?Ronald S. Bultje wrote:
>>>> ?ffplay rtsp://qtss1.bgsu.edu/wfal08.sdp fails:
>>>>> [rtsp @ 0x1032600]Could not find codec parameters (Audio: aac, 22050
>>>>> Hz, 2 channels, s16)
>>>>> rtsp://qtss1.bgsu.edu/wfal08.sdp: could not find codec parameters
>>>>> because AVCodecContext->frame_size is 0. Who should set it? Demuxer?
>>>>> how/where?
>>>>> ?AFAIK, for RTP the frame size is set by the decoder, not by the
>>>> demuxer.
>>> Aha, you're right, it just takes very long. OK, bugreport then: the file
>>> plays twice as fast as it should (Quicktime does it OK), both with ffAAC
>>> and
>>> with faad. Care to look into this? Want a issue tracker entry?
>> Well, this looks like an AAC decoder issue: vlc plays the stream correctly,
>> and sees 2 channels at 44100Hz, but ffmpeg sees 2 channels at 22050Hz.
>> The funny thing is that the server is also confused about this, because the
>> SDP contains a line saying:
>> ? ? ? ?a=rtpmap:96 mpeg4-generic/22050/2
>> I guess it's the AAC SBR thing (someone told me that is "fakes" the sample
>> rate, doubling it... But I do not know this stuff, so I really have no
>> idea if this is the problem or not). Is SBR supported by ffmpeg?
>> Anyway, this is something for people that understand AAC better than me...
>> Maybe opening an issue on roundup (with AAC mentioned in the subject) or
>> starting a new thread that explicitly mentions AAC would help.
> I've got a reproducible case where ?ffmpeg produced SBR, but couldnt decode
> it (garbled).
> it was libfaac with ffmpeg v18867.
> The newer ffmpeg v19134 doesnt accept -libfaac... haven't tried -faac; I'm
> using the faac.exe tool directly to avoid the issue.
> If someone is interested in pursuing the SBR weirdness I can provide files.

I'm a bit confused here. ffaac does not support SBR decoding at all.
faac does not support SBR encoding at all.


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