clips over each other cause excess work, performance drops
Submitted by Jeff F.T.
Assigned to Jeff F.T.
Created attachment 170361
If you position clips over each other in different tracks (see screenshot), you will notice a significant performance hit when rendering or when playing back.
This would be expected if one of the clips was transparent, but when the opacity curves are set to 100%, this shouldn't happen.
This is especially visible in rendering (since everything happens in "slow motion", you can see it spends much more time when there are clips on top of each other).
It also seems to affect live playback in the timeline.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=629784