[XviD-devel] 32Bit input pin / Alpha

Christoph Lampert chl at math.uni-bonn.de
Fri Jul 18 21:39:33 CEST 2003


two part answer: 
a) There's no support for alpha-masking for textures etc. in XVID, because
those are not in "Simple" or "Advanced Simple" Profile, and XVID
implements those. 

b) There could of course be a input routine to convert 32bit RGBA to the
usual YUV, where the alpha channel is somehow used as a mask or so. You
can easily use RGB 24bit input routine for this, and just multiply by the
alpha value or something. But the result would not be alpha-channeled or
so, of course. Just ordinary picture which is calculated from RGB + alpha.


On Fri, 18 Jul 2003, Florian Schaper wrote:
> Hello,
> for my current Project (using DirectShow) I need a video-codec with an 32Bit
> input pin (to save an alpha channel).
> Most Videocodec's provide an 32Bit output pin (xvid thankfully already set's
> the alpha value to 255, thanks guy's ) but not an 32Bit input pin (talking
> still about directShow).
> I understand, that most people won't need alpha in their movies anyway but
> hey, here I am.
> The mpeg4 standard reads somewhat promissing, alpha for textures and so on,
> but I found no codec that would implement it.
> I don't know that much about what you guy's are fighting with, so all thats
> left for me is simply to ask you how difficult it would be to "upgrade" the
> existing xvid source to encode an 8Bit alpha channel as well? Is there no
> 32bit 'in', simply because nobody saw a need there to implement it? Or are
> there other (technical) reasons ? (besides maintaining more sections of
> code).
> Currently I'm using the huffyuv codec but since it work's lossless files get
> to big and performace is crappy.
> If there is no way xvid will support this in imminent future is there
> another codec that might fit my needs? (fast [playback that is] & small,
> like alway's)
> Thanks for your help
> ./regards
> Florian Schaper
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> XviD-devel at xvid.org
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