[FFmpeg-devel] AAC decoder round 5

[Michael Niedermayer]

On Fri, Aug 08, 2008 at 03:38:06PM +0100, Robert Swain wrote:
> 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]. :)

[8][51].might lead to slow addressing of the contents due to *51 instead
of <<6

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I wish the Xiph folks would stop pretending they've got something they
do not.  Somehow I fear this will remain a wish. -- M?ns Rullg?rd
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20080808/891bec9c/attachment.pgp>