[FFmpeg-devel] MP4A-LATM support?
Fri Nov 13 12:53:50 CET 2009
Reimar D?ffinger wrote:
> On Fri, Nov 13, 2009 at 12:33:40PM +0100, Luca Abeni wrote:
>> 5) how can the muxer know if the bitstream is "regular AAC" or LATM?
>> I think we need a "fake" codec ID (CODEC_ID_LATM, or something like
>> this) for identifying LATM streams. When the AAC stream is transformed
>> in LATM (or vice-versa) by the bitstream filter, the codec ID is changed
>> from CODEC_ID_AAC to CODEC_ID_LATM (or vice-versa).
> To my knowledge the way this currently works (e.g. with
> h264_mp4toannexb_bsf) is that the muxer just assumes the user will have
> remembered to insert the right filter.
> Obviously that leaves room for improvement...
Yes, but there are muxers (I have the RTP muxer in mind :) that support both
"regular AAC" bitstreams and LATM bitstreams (packetising them in different
ways, according to different RFCs).
So, the muxer must somehow know if the user inserted the filter (and LATM
packetisation has to be used) or not (and AAC packetisation has to be used).
The RTP-LATM patch that has been submitted some time ago added a flag to
AVFormatContext for this... I do not know which solution is better.
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