[FFmpeg-devel] AAC decoder round 5

[Robert Swain]

2008/8/8 Robert Swain <robert.swain at gmail.com>:

[...]

> So, it seems the issue is not MAX_CHANNELS so much as the window group
> and scalefactor band arrays. I'm going to check the cases for maximum
> number of scalefactor bands per window group as I expect it may be
> beneficial to flatten these two indices.

const uint8_t ff_aac_num_swb_1024[] = {
    41, 41, 47, 49, 49, 51, 47, 47, 43, 43, 43, 40
};

const uint8_t ff_aac_num_swb_128[] = {
    12, 12, 12, 14, 14, 14, 15, 15, 15, 15, 15, 15
};

For the long transform, there can only be 1 window group so the worst
case there is 51 scalefactor bands in total.

For the short transform there can be up to 8 window groups (i.e. each
group containing only one short window) each with up to 15 scalefactor
bands, totalling 120 scalefactor bands maximum for this case.

So, instead of [8][64] we could have [120] which is quite a bit better
but maybe it would obfuscate the code a lot, I'll ponder this now. At
the very least we can have [8][51]. :)

Rob