[FFmpeg-soc] [soc]: r2719 - nellyenc/nellymoserenc.c

[Michael Niedermayer]

On Tue, Jul 29, 2008 at 10:34:04AM +0200, Bartlomiej Wolowiec wrote:
> On środa, 9 lipca 2008, Michael Niedermayer wrote:
> > On Tue, Jul 08, 2008 at 11:17:06PM +0200, Bartlomiej Wolowiec wrote:
> > > On poniedziałek, 7 lipca 2008, Michael Niedermayer wrote:
> > > > On Mon, Jul 07, 2008 at 10:55:16PM +0200, Reimar Döffinger wrote:
> > > > > Hello,
> > > > >
> > > > > On Mon, Jul 07, 2008 at 10:21:38PM +0200, Bartlomiej Wolowiec wrote:
> > > > > > On poniedziałek, 7 lipca 2008, Robert Swain wrote:
> > > > > > > 2008/7/7 bwolowiec <subversion at mplayerhq.hu>:
> > > > > > > > Author: bwolowiec
> > > > > > > > Date: Mon Jul  7 16:41:50 2008
> > > > > > > > New Revision: 2719
> > > > > > > >
> > > > > > > > Log:
> > > > > > > > use ff_sine_window_init
> > > > > > > >
> > > > > > > >
> > > > > > > > Modified:
> > > > > > > >   nellyenc/nellymoserenc.c
> > > > > > > >
> > > > > > > > Modified: nellyenc/nellymoserenc.c
> > > > > > > > ===============================================================
> > > > > > > >==== ====== ===== --- nellyenc/nellymoserenc.c    (original) +++
> > > > > > > > nellyenc/nellymoserenc.c    Mon Jul  7 16:41:50 2008 @@ -116,10
> > > > > > > > +116,13 @@ static av_cold int encode_init(AVCodecCo
> > > > > > > > dsputil_init(&s->dsp, avctx);
> > > > > > > >
> > > > > > > >     /* Generate overlap window */
> > > > > > > > -    if (!sine_window[0])
> > > > > > > > -        for (i=0 ; i<256; i++) {
> > > > > > > > -            sine_window[i] = sin((i + 0.5) / 256.0 * M_PI) /8;
> > > > > > > > +    if (!sine_window[0]){
> > > > > > > > +        ff_sine_window_init(sine_window, 128);
> > > > > > > > +        for (i=0; i<128; i++) {
> > > > > > > > +            sine_window[i] /= 8.0;
> > > > > > >
> > > > > > > This isn't thread safe. You must merge the /8 into some other
> > > > > > > calculation.
> > > > > >
> > > > > > Hmm.. yes, you're right. Unfortunately, I don't see now where it
> > > > > > can be calculated. If I don't calculate it in init I will have to
> > > > > > calculate it additionally in every encode_tag, it isn't a good
> > > > > > idea.  Maybe it's better to use previous version and don't use
> > > > > > ff_sine_window_init...? or maybe (in my opinion a bit unnatural)
> > > > > > such a solution:
> > > > > > ff_sine_window_init(tmp_sine_window, 128);
> > > > > > for (i=0; i<128; i++) {
> > > > > >   sine_window[i] = tmp_sine_window[i] / 8.0;
> > > > > >   sine_window[255-i] = sine_window[i];
> > > > > > }
> > > > >
> > > > > Just use your original code on some per-thread buffer (stack or heap
> > > > > depending on size) and then memcpy it over.
> > > >
> > > > Please everyone stop scaring me ...
> > > >
> > > > pval = -pow(2, pows[j]/2048);
> > > > tmp = s->mdct_out[i*NELLY_BUF_LEN + j] / pval;
> > > >
> > > > above is in the current code, that will happily take a /8
> > > > besides it obviously should be a * not a / pval, / is slow
> > > >
> > > > [...]
> > >
> > > Do you think of something like this?
> >
> > yes, next get rid of the pow() thats slow as well ...
> >
> > > Or maybe instead of this additional calculations it can be better
> > > calculated once while initialization... ?
> >
> > initialization of what?
> > The window is supposed to be shared between codecs and cannot be changed
> > besides what additional calculations? "pows" are differntially coded
> > adding 3*2048 at the begin really does not matter, especially if you
> > do a pow()in the inner loop.
> >
> > [...]
> 
> After short break I will try to spend much time on writing nellymoser encoder.
> 
> I don't see exactly how to make it using 3*2048 values...
> Can you give me a bigger clue how to do it?

First you get rid of the pow(), that is you do not in the innermost loop
calculate pow(value that does not change) all the time!

After that, you will have the values that came out of the pow() with which
you did divide, these values then should be multiplied by the scale factor
OUTSIDE the loop. (they likely will be in an new array ...)

Is that clear?

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

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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