[Mp4-tech] [MPEG-4 decoder AAC] time delays in SBR decoder

[Andrzej Kaczor]

Hi all,
There are time delays in the function "sbr_dec":
void sbr_dec ()
{
    /* */
    CalculateSbrAnaFilterbank(
                             lowBandBuffer[channel] + 0,           //input
                             codecQmfBufferReal[channel][8],    //re_output
                             codecQmfBufferImag[channel][8],   //im_output
                                           );                                  // 6+2 windows
    generateHF(
                             codecQmfBufferReal[channel] + 2,     //re_input
                             codecQmfBufferImag[channel] + 2,    //im_input
                             sbrQmfBufferReal[channel] + 2,         //re_output
                             sbrQmfBufferImag[channel] + 2,        //im_output
                                           );                                  // 2 windows
    /* etc. */
    //calculateSbrEnvelope
   //CalculateSbrSynFilterbank
}
I don't understand the purpose of those time delays. What are they used for? Why 2 and 6+2?
Best Regards,
Andrzej Kaczor
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