AAC decoder

After 9 rounds review by Michael Niedermayer and approximately 3 months of gruelling code monkey labour by myself (with guidance from Kostya and others) the FFmpeg AAC decoder is finally in FFmpeg trunk! Huzzah!

The pain doesn’t stop there though. I expect I will receive some bug reports and such in the near future. I will be working on integrating my SBR code which hopefully won’t take too long as it is all written.

I have just finished some patches to port the decoder from using the old ff_imdct_calc() and vector_fmul_add_add() functions to using Loren Merritt’s ff_imdct_half() (which takes advantage of MDCT symmetries) and vector_fmul_window() (which allows windowing with only the middle half of the IMDCT-ed coefficients). With these patches I observe an ~10% performance increase.

To top it all off, I decided I should benchmark against FAAD as well. The FFmpeg AAC decoder has an ~135% performance increase from FAAD. Cool, eh?