[Mp4-tech] Re: [Audio] AAC LC problem with mannual decoding of raw_data_block()

[Ralph Sperschneider]

goutham vaidhya wrote:
> hi all,
>   In aac lc profile i just tried to decode the raw data stream manually.
>   In standard it states that we will get the spectral values till    
>   max_sfb, which can be less then num_swb(table 8.4 - 8.16 of mpeg2 aac).
>   So i got 640 spectral values after hufmman decoding. BUt for doing 
> IMDCT we 
>   need 1024 samples.
>   Can anybody pls tell me what we should fill in the remaining 
> spectral values.
>   Pls tell me where in the specification does this is mentioned
>   tnx in advance.
>
> -- 
> Have a NICE day

Dear Goutham Vaidhya,
ISO/IEC 13818-7:2005, subclause 8.3.2.6 (Spectral Data Parsing and 
Decoding) states:
"
The spectral data is recovered ... It consists of all the non-zeroed 
coefficients remaining in the spectrum or spectra, ...
"
Furthermore, ISO/IEC 13818-7:2005, subclause 9.3 (Decoding Process) states:
"The spectral information for all scalefactor bands at and above 
max_sfb, for which there is no section data, is zero."
Those statements should clarify your question.
Best regards,
Ralph
-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
Fraunhofer IIS                  | Fax:   +49 9131 776 398
Am Wolfsmantel 33               | mailto:ralph.sperschneider iis.fraunhofer.de
D 91058 Erlangen                | http://www.iis.fraunhofer.de/amm/