This has been bugging me for years.
If you make a mask with bezier vertexes, you get handles on both sides of the vertex, right.
Now, when you create the mask, or create a beier vertex through conversion methods, both of the handles are connectd, meaning they move in unison - that is their default behaviour. You can disconnect them by dragging a hande with Alt pressed - from now on the handles are diisconnected and you have to move each separately.
That is all fine, that is the expected behaviour.
Now,if you have a mask and you animate its shape, the properties of the vertexes are taken from the previous keyframe, as they should.
So you create the mask on frame 0 - all your vertexes are bezier vertexes wiith connected handles.
Move to frame 10, edit the mask - all your vertexes are still beziers with connected vertexes, fine.
Move to frame 20, edit - still fine, all handles are connected.
But now create a keyframe between two existing keyframes, let's say frame 13 - all of a sudden all of the handles in all vertices become disconnected!!! They no longer move in unison, you have to move each one separately.
But if you go to frame 30, or even 21 (as long as it's not between two existing keyframes) - the handles are connected again.
It's been like this ever since I can remember.
Is there a reason for this behaviour? Can it be switched off?
I mean disconnected handles are useless - there are very rare situations when I need them, most of the time I need connected handles, because I want the mask to be smooth - why are they breaking every time I want to adjust the mask between two keyframes???
Well that's really weird. I've never really noticed this: and playing around just now I had inconsistent behaviour - sometimes when adding a keyframe between existing ones seemed to keep the handles connected, sometimes it disconnected them into two discontinuous handles.
My workflow when masking/matting stuff (or anything manually tracked w keyframes, like tracking a light with a null to add a lensflare to) has always been to do the broad keyframing first - keyframing just the big moves, or every 50 frames or whatever, and then gradually refining by adding keyframes between the existing ones... and I've never noticed this problem before. Huh.
Alt-dragging a handle has always disconnected it from its partner ... but what's the shortcut/tool for reconnecting broken handles on a vertex? I actually don't know