[Matroska-devel] AAC and SBR

Zen aaa at aaaa.com
Wed Apr 26 09:17:20 CEST 2006


This question is not specific to MKV, but I think I have a good group of 
video and audio experts here ;-)

On the matroska CodecID page, there are AAC with or without SBR.
I though that you know how to detect SBR ;-)

in the file aac_common.cpp, I found this :
******
   if (size == 5) {
     output_sample_rate = aac_sampling_freq[(data[4] & 0x7f) >> 3];
     sbr = true;
   } else if (sample_rate <= 24000) {
     output_sample_rate = 2 * sample_rate;
     sbr = true;
   } else
     sbr = false;
******

I don't understand where come from this "size" of 5, why do you do this?
And for other sizes, is the sample_rate detection (>24K or not) is the 
only mean to detect SBR???

Zen, developper of MediaInfo



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