[Ffmpeg-devel] Dubious field in AAC-ADTS

Måns Rullgård mru
Fri Jun 10 19:02:22 CEST 2005

"Nico Sabbi" <nsabbi at fastwebnet.it> writes:

>>"Nico Sabbi" <nsabbi at fastwebnet.it> writes:
>>> Hi,
>>> I don't fully understand what's the meaning of the field 
>>> "no_raw_data_blocks_in_frame" described here:
>>> http://www.audiocoding.com/modules/wiki/?page=ADTS
>>> Is it the number of audio frames carried in the current 
>>> ADTS packet or what else? If not, can I always assume that
>>> an ADTS packets always carries exactly 1 AAC frame?
>>That field specifies the number of raw_data_block elements that
>>follow.  Each raw_data_block decodes into 1024 or 960 samples for each
>>channel.  See ISO 14496-3, section 4.5.2.  Does this answer your
> yes: crystal-clear as usual :)
> BTW, in the sources of libfaad2 there's a comment stating that
> a the 2-bits field present in the specs of ADTS-4 (emphasis
> IIRC) but not in ADTS-2 were removed 
> from the specs of ADTS-4, effectively making the two frames 
> syntaxes identical, except for the ID field. 

Yes, the emphasis field was removed in Corrigendum 1 to 14496-3.  ISO
will actually give you this document in exchange for nothing but your

> Did you ever find some sample coded with 'emphasis'?

Not that I know of.  I haven't looked for it, though.

M?ns Rullg?rd
mru at inprovide.com

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