[FFmpeg-devel] decSpecificInfo for aac lc in mp4 file container

Van Echaute, Pete GE EntSol, SensInsp Pete.VanEchaute
Fri Aug 1 17:01:03 CEST 2008

I am using FFMPEG with FAAC and FAAD libs to create an MP4 file
container that contains stream copies of MPEG4 and AAC LC.  The one
thing I saw was that the decSpecificInfo isn't being setup correctly and
seems to be very important to analyzers and players.  I have seen
examples of files having this set to 0x12 0x10 and also 0x11 0x90.  I
don't know which is correct or if another one should be used.
libavformat/movenc.c is simply copying a value if it is set.  The
libfaac files are not setting this value.
I am able to set it up on my own during the initialization steps as
         codec->extradata_size  = 2;
         codec->extradata       = av_malloc ( codec->extradata_size +
         codec->extradata[0]    = 18;   // 0x12
         codec->extradata[1]    = 16;   // 0x10
//         codec->extradata[0]    = 17;    // 0x11
//         codec->extradata[1]    = 144;  // 0x90
But, what should the value of this decSpecificInfo be for my AAC LC

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