Wipe ell,RGB Multit transition work funny with alpha clips

[Zoltán]

when setting transition mode to Wipe Ellipse (edit: and RGB) , clips with alpha channels are not wiped as I would expect.
the source clip can be seen until it is ejected (and then cut) if the destination clip has alpha.

to show you what I mean:

phpBB [video]

edit:
also the multitask transition seems to cut the layers' alpha channel completely while transition.

phpBB [video]

[Zoltán]

The time switcher transition seems to keep the source clip in place, thus a destination clip with alpha lets the source look thru, so the transition look different if transitioning to alpha clip as it looks when transitioning to non alpha.

(RGB, Shift RGB, and some of these look funny with alpha IMO, because the source is not processed the same way as the destination clip.)

[Joris]

Yes, this is because transitions are actually also blends and they work by increasingly blending the incoming clip with the outgoing.

To get proper results, this means the outgoing clip is not faded out. Otherwise, you'd see the layers beneath it bleed through at some point or other.

So the outgoing clip is kept at full opacity, until the blend is completed and only the incoming clip is visible. Then it's ejected.

Of course, when you have alpha in the incoming clip, this won't work, because the incoming clip will never completely cover the outgoing. This results in the hard cut you see. So a while back, around 4.1.8 I believe, we modified the Alpha transition to work correctly for clips with an alpha channel. Alpha is the only transition that will work correctly for this.

Clip transitions are actually quite a bees' nest. You'd think it would be dead-easy, but with all the different transition types and blends, there is no one-size-fits-all solution. I'll be happy to shoot holes in whatever you come up with, if you think you can do better