[Mp4-tech] Re: [audio] AAC bitstream - headers

[Ralph Sperschneider]

Anubrata Chkarabarti wrote:
> Hi
> I'm writing AAC analyzer/decoder. Here are my questions:
> 1. How do I get to know header of the supplied AAC file, i.e whether
> will it have ADIF or ADTS or no header?
> 2. Do I need to parse AudioSpecificConfig all the time? Does this depend
> on the presence of ADIF/ADTS headers?
> 
> Regards
> Anubrata
> 
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Dear Anubrata,
if you get header-less AAC data you cannot do much with it unless you know at 
least the sampling rate.
To check for ADIF you can look for the adif_id at the begin of the file.
To check for ADTS you can try to synchronize (using the syncword and some 
subsequent information).
In all cases mentioned above there is no AudioSpecificConfig, since those are 
MPEG-2 centric. An AudioSpecificConfig shows only up in MPEG-4 centric cases, 
e.g. while using latm or the mp4 file format.
Best regards,
Ralph
-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
Fraunhofer IIS                  | Fax:   +49 9131 776 398
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