[FFmpeg-devel] [PATCH] RDFT for Bink and QDM2

[Michael Niedermayer]

On Sat, Jan 17, 2009 at 01:29:13PM -0500, Alex Converse wrote:
> Attached is my RDFT patch with all the feedback applied. Also attached
> is a patch that makes use of it in QDM2 decoding. I thought I had
> unwrapped the math perfectly but it looks like things changed for the
> better.
> 
> Also new is a flag for FFT sign convention. This is because the
> inverse transform is not the same as the forward transform with the
> opposite sign convention, scaled.
> 
> The reference files are decoded with the binary coder from the qt63 dlls.
> 
> $ tests/tiny_psnr ../qdm2/nadasurf_popular_dl.wav old.wav 2 0 44
> stddev: 1305.89 PSNR: 34.00 bytes: 39632896/ 39632896
> $ tests/tiny_psnr ../qdm2/nadasurf_popular_dl.wav new.wav 2 0 44
> stddev: 1145.39 PSNR: 35.14 bytes: 39632896/ 39632896
> $ tests/tiny_psnr ../qdm2/switzler084d_dl.wav old.wav 2 0 44
> stddev:  377.46 PSNR: 44.78 bytes: 20660224/ 20660224
> $ tests/tiny_psnr ../qdm2/switzler084d_dl.wav new.wav 2 0 44
> stddev:  305.00 PSNR: 46.63 bytes: 20660224/ 20660224
[...]
> +/**
> + * Sets up a real FFT.
> + * @param nbits           Log2 of the length of the input array
> + * @param inverse         If TRUE, perform the inverse of the transform
> + * @param sign_convention The sign of j of the forward FFT.
> + */
> +int ff_rdft_init(RDFTContext *s, int nbits, int inverse, int sign_convention)
> +{
> +    int n = 1 << nbits;
> +    int i;
> +    const double theta = sign_convention*(1-2*inverse)*2*M_PI/n;
> +
> +    s->nbits           = nbits;
> +    s->inverse         = inverse;
> +    s->sign_convention = sign_convention;
> +
> +    if (ff_fft_init(&s->fft, nbits-1, (sign_convention==1) ^ inverse) < 0)
> +        goto fail;
> +

> +    s->tsin = av_malloc((n>>2) * sizeof(FFTSample));

i do prefer that no tables are duplicated

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

> ... defining _GNU_SOURCE...
For the love of all that is holy, and some that is not, don't do that.
-- Luca & Mans
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