Hi, On Mon, Aug 4, 2014 at 11:42 AM, Clément Bœsch <u...@pkh.me> wrote:
> On Mon, Aug 04, 2014 at 11:17:29AM -0400, Ronald S. Bultje wrote: > > Hi, > > > > On Sun, Aug 3, 2014 at 4:27 PM, Clément Bœsch <u...@pkh.me> wrote: > > > > > This removes the avcodec dependency and make the code almost twice as > > > fast. More to come. > > > > > > The DCT factorization is based on "Fast and numerically stable > > > algorithms for discrete cosine transforms" from Gerlind Plonkaa & > > > Manfred Tasche (DOI: 10.1016/j.laa.2004.07.015). > > > > > > I have no comments on the patch itself, but can you explain why we're > > re-implementing a custom f/idct rather than using the one provided in > > lavcodec? It seems to me that going from fixedpoint/simd'ed to float/c > > would be slower, not faster, so there must be more to this patch than > what > > I'm getting from it... > > > > OK so as said in private, I didn't find an accurate (not wrongly "JPEG" > like I originally said) 16x16 DCT in libavcodec. > > You suggested to use the HEVC or VP9 DCT. That's indeed one solution, but > we currently have only IDCT for those (AFAIK), and I needed a float > implementation. You mean forward. idct is inverse, fdct is forward, such that idct(fdct(data[][])) =~ data[][]. You can use the forward transforms provided in libvpx (for vp9) or x265 (hevc), they're quite precise, and already optimized. Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
