[FFmpeg-devel] [PATCH] 1D DCT for dsputil
Alex Converse
alex.converse
Sat Jan 16 08:30:53 CET 2010
On Sat, Jan 9, 2010 at 10:05 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Fri, Jan 08, 2010 at 12:43:48PM -0500, Alex Converse wrote:
>> On Fri, Jan 8, 2010 at 10:12 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> > On Fri, Jan 08, 2010 at 01:02:19AM -0500, Alex Converse wrote:
>> >> On Tue, Dec 22, 2009 at 8:04 PM, Alex Converse <alex.converse at gmail.com> wrote:
>> >> > 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.
>> >> >
>> >>
>> >> As promised...
>> >
>> > [...]
>> >> +av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
>> >> +{
>> >> + ? ?int n = 1 << nbits;
>> >> +
>> >> + ? ?s->nbits ? ?= nbits;
>> >> + ? ?s->inverse ?= inverse;
>> >> +
>> >> + ? ?s->data = av_malloc(sizeof(FFTComplex) * 2 * n);
>> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?^^^^^
>> >
>>
>> This should be FFTSample.
>>
>> >> + ? ?if (!s->data)
>> >> + ? ? ? ?return -1;
>> >> +
>> >> + ? ?if (ff_rdft_init(&s->rdft, nbits+1, inverse) < 0)
>> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?^^^^^^^
>> >
>> > doesnt look like 1*N to me
>> > am i missing something?
>> >
>>
>> The RDFT initializes an FFT of size nbits-1.
>
> yes and if iam not mistaken that should be nbits-2
> your code is 2x more efficient than daniels but its still by a factor of 2
> worse than what it should be
>
> Maybe iam missing something but the sample code in numerical recipes should
> be useable?
>
I see what you are saying here.
I'm not going to get a chance to play with this again until SBR is
ready. (Hopefully very soon but that's another story.)
So some bink enthusiast is going to have to step in here and finish it
unless you all mind waiting.
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