[FFmpeg-devel] [PATCH] 1D DCT for dsputil

Alex Converse alex.converse
Wed Dec 23 02:04:39 CET 2009

On Tue, Dec 22, 2009 at 6:25 AM,  <pross at xvid.org> wrote:
> On Mon, Dec 21, 2009 at 02:02:00PM -0500, Daniel Verkamp wrote:
>> Hi,
>> In an effort to get at least some parts of the Bink patch committed, I
>> am splitting it into separable pieces.
>> This is a one-dimensional floating-point DCT used by Bink audio. ?The
>> actual code was written by Peter Ross.
>> The comments I myself have about this code:
>> - Should it be using math.h cos()/sin() or some lookup table approach?
>> - Can there be a test written? (I don't know enough about the math
>> involved to write a sane test...)
> Thanks for taking the time to split the patch.
> Note that the algorithm here is inefficient. It requires a 2*N FFT,
> whereas there are ways of achieving this with 1*N FFT. Michael posted
> some info on this many months ago.

I had a 1-D 1*N DCT but it generated the transpose (i.e.
uninterleaved). I can dig it up when I come back from xmas holiday if
you are interested.

> IIRC, optimising the DCT was the only outstanding comment raised against
> my earlier Bink audio patch. Reported audio glitches were fixed.

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