On Sun, 2 Dec 2001, Billy Biggs wrote:
> > > I still think that using DMA is essential for all drivers if the
> > > images doesn't require some conversion. I guess I'd be worried
> > > about drivers which require scanlines to be 32bit aligned. Too bad
> > > the Xv API doesn't allow for that. (or am I on crack again)
> >
> > I'm not sure what you mean. Pretty much everything always needs to be
> > 32 bit aligned. mpeg scanlines are always multiples of 16 pixels
> > anyhow.
>
> Well for planar formats, 720 luma samples is 720 bytes, and that just
> doens't align nicely. But yes, if you're using 4:2:2, 720*2 is nice and
> round.
I'm not following you. 720 luma is 128 bit aligned.
> I find it interesting that all these overlays only use 4:2:2. Do you
> think I should move the conversion into my app and save them the trouble
> (and also improve my OSD compositing)? Sounds like a win to me.
The drivers are usually just loop unrolled C (and sometimes not even
loop unrolled). If you're using SSE or MMX, I'm pretty sure you can
do the 4:2:2 conversion quicker. Some drivers really do 4:2:0 though
and more will in the future so you should make 4:2:2 conversion in your
software optional and probably not default.
Mark.
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