[FFmpeg-devel] [PATCH] Generic sine window init function

[Michael Niedermayer]

On Sun, Jun 22, 2008 at 01:15:22PM +0100, Robert Swain wrote:
> 2008/6/22 Michael Niedermayer <michaelni at gmx.at>:
[...]
> > [...]
> >> Index: libavcodec/imc.c
> >> ===================================================================
> >> --- libavcodec/imc.c  (revision 13854)
> >> +++ libavcodec/imc.c  (working copy)
> >> @@ -102,8 +102,9 @@
> >>          q->old_floor[i] = 1.0;
> >>
> >>      /* Build mdct window, a simple sine window normalized with sqrt(2) */
> >> +    ff_sine_window_init(q->mdct_sine_window, COEFFS);
> >>      for(i = 0; i < COEFFS; i++)
> >> -        q->mdct_sine_window[i] = sin((i + 0.5) / 512.0 * M_PI) * sqrt(2.0);
> >> +        q->mdct_sine_window[i] *= sqrt(2.0);
> >>      for(i = 0; i < COEFFS/2; i++){
> >>          q->post_cos[i] = cos(i / 256.0 * M_PI);
> >>          q->post_sin[i] = sin(i / 256.0 * M_PI);
> >> Index: libavcodec/cook.c
> >> ===================================================================
> >> --- libavcodec/cook.c (revision 13854)
> >> +++ libavcodec/cook.c (working copy)
> >> @@ -239,9 +239,9 @@
> >>        return -1;
> >>
> >>      /* Initialize the MLT window: simple sine window. */
> >> -    alpha = M_PI / (2.0 * (float)mlt_size);
> >> +    ff_sine_window_init(q->mlt_window, mlt_size);
> >>      for(j=0 ; j<mlt_size ; j++)
> >> -        q->mlt_window[j] = sin((j + 0.5) * alpha) * sqrt(2.0 / q->samples_per_channel);
> >> +        q->mlt_window[j] *= sqrt(2.0 / q->samples_per_channel);
> >
> > The window should not be scaled by sqrt(2) there are plenty of other places
> > where the sqrt(2) could be applied.
> > and it should not be in the context but static and shared
> > (of course that is not really your job to do so the patch is ok if you dont
> > want to work on that)
> 
> It's OK. I'll do it. I don't mind a bit of monkey work now and again. :)
> 
> I actually have some improvements. As these normalisation factors are
> always that, how about adding another argument and multiplying by the
> normalisation factor within the init function? This could also be done
> for ff_kbd_window_init() as well which would solve that non-thread
> safe situation in aac.c. See attached.

I would like to share the tables between codecs!
If each codec puts its normalisation factors in the window
then they cannot be shared as they are not identical.

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

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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