[FFmpeg-devel] [RFC] AAC Encoder

[Gabriel Bouvigne]

Michael Niedermayer a ?crit :
>>            switch(last_window_sequence){
>>            case ONLY_LONG_SEQUENCE:
>>                win[ch] = switch_to_eight ? LONG_START_SEQUENCE : ONLY_LONG_SEQUENCE;
>>                grouping[ch] = 0;
>>                break;
>>            case LONG_START_SEQUENCE:
>>                win[ch] = EIGHT_SHORT_SEQUENCE;
>>                grouping[ch] = pch->next_grouping[ch];
>>                break;
>>            case LONG_STOP_SEQUENCE:
>>                win[ch] = ONLY_LONG_SEQUENCE;
>>                grouping[ch] = 0;
>>                break;
>>            case EIGHT_SHORT_SEQUENCE:
>>                win[ch] = switch_to_eight ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE;
>>                grouping[ch] = switch_to_eight ? pch->next_grouping[ch] : 0;
>>                break;
>>            }
>>            pch->next_grouping[ch] = window_grouping[attack_n];
> 
> 
> this is limited to 9 of 256 possible groupings, not to mention that i have my
> doubts about the optimality of the highpass based selection.

For the only 9 possible grouping, I agree that it's not optimal (please 
remember that the 3gp reference model is provided by Coding Technologies 
which also need to be able to sell their own encoder).
Regarding the highpass method, if the highpass freq is properly choosen, 
it's a method that demonstrated its usefullness. Its main drawback is 
usually the computation time compared to spectrum-based methods which 
can often be done using data that is already computed.

Regards,

-- 
Gabriel Bouvigne
www.mp3-tech.org
personal page: http://gabriel.mp3-tech.org