[FFmpeg-devel] [PATCH] ALAC Encoder

Jai Menon realityman
Sun Aug 17 20:31:46 CEST 2008


Hi,

On Sunday 17 Aug 2008 6:45:17 pm Michael Niedermayer wrote:
> On Sun, Aug 17, 2008 at 09:09:00AM +0530, Jai Menon wrote:
> > Hi,
> >
> > On Sunday 17 Aug 2008 8:05:14 am Michael Niedermayer wrote:
> > > On Sun, Aug 17, 2008 at 04:14:43AM +0530, Jai Menon wrote:
>
> [...]
>
> > > > +static void alac_stereo_decorrelation(AlacEncodeContext *s)
> > > > +{
> > > > +    int32_t *left = s->sample_buf[0], *right = s->sample_buf[1];
> > > > +    int32_t tmp;
> > > > +    int i;
> > > > +
> > > > +    for(i=0; i<s->avctx->frame_size; i++) {
> > > > +        tmp = left[i];
> > > > +        left[i] = (tmp + right[i]) >> 1;
> > > > +        right[i] = tmp - right[i];
> > > > +    }
> > > >
> > > > +    s->interlacing_leftweight = 1;
> > > > +    s->interlacing_shift = 1;
> > >
> > > i do not belive this is optimal
> >
> > It may not be optimal in the sense that I do not adaptively select the
> > decorrelation scheme, but this is just the first iteration which aims at
> > getting a basic encoder into svn. And it is better than doing no
> > deorrelation. I did initially try out an adaptive approach but the
> > difference in compression wasn't that great. I'm looking into how this
> > can be done in a better manner. Till then, I was hoping if we could go
> > with this.
>
> see the pca.c/h i posted in a reply to ramiro a few days ago
> it might be worth a try ... (and dont hesitate to ask if you have no clue
> on how to use it ...)
>

I'd be lying if I said I understood much. The math seems okay but how does 
this fit in with decorrelation?


Regards,

Jai Menon




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