Using videomixer and alpha channel

[Sebastian Dröge]

On Mo, 2013-11-25 at 10:26 +0100, Eric Trousset wrote:

> > Are you making sure that the video input to videomixer is still having the
> > alpha channel, i.e. there's no videoconvert element in front of it that
> > converts it to something without alpha channel?
> > 
> > The blending code in videomixer should use the alpha channel already.
> 
> Yes I had a videoconvert element. So I removed it but still, it seems
> the pixel alpha is not taken into account. I can see the checker
> background only if I set the pad's "alpha" property to some value.

That's weird and sounds like a bug. The blending operation done by
videomixer for ARGB/AYUV currently is
destination = source*alpha + destination*(1-alpha)
where alpha is the alpha property of the pad multiplied with the alpha
channel of source at the current position.

Should get a bug report I guess.

> > > Also, I am using imagefreeze to display a still image. Is there a way to make
> > this element to ask the source for a new image at some point?
> > 
> > There isn't, but it could be implemented with some custom event. Or maybe
> > all this should just handle the request-keyunit event. Nothing is
> > implemented yet for that.
> 
> 
> That would be a great feature :)

Could you file a feature request at http://bugzilla.gnome.org against
GStreamer for that so it doesn't get lost?

-- 
Sebastian Dröge <sebastian at centricular.com>
Centricular Ltd - http://www.centricular.com
Expertise, Straight from the Source
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