I've seen a couple of tutorials on best practice for rotoscoping and they suggest drawing the mask on a separate solid layer, and tracking the object to help the mask stay where you want it. However, they didn't go into enough details for a beginner like me.
Tracking - I tracked the object I wanted to roto (using stabilize as track type, and ticking boxes for position, rotation and scale so there were 2 joined tracking points). The target was the footage layer. Once that was done, I copied & pasted the tracker from the footage layer to the solid so they were both stabilized and in sync. Once I'd finished keyframing the mask, how do I go about undoing the tracking stabilization on both? I tried deleting the trackers from each but it all went out of sync and finally crashed AE.
Drawing masks on a separate solid - what do I apply it to the footage, once it's done? Copy and paste it to the footage layer or is using trackmatte the way to go?
Create a new comp with your non-stabilised footage and paste the solid matte layer into it and delete the track and motion data.
Create a new comp with your non-stabilised footage and create a new solid layer and paste your keyframed mask data on to this.
If you're going to do a lot of roto it may be worth your while to take the time to learn Mocha, a version of which ships with after effects, its planar tracking software and has a lot of uses, one of which is rotoscoping.
Also don't try and draw masks for the entire object if parts of it move in different directions, like a human for example. Have separate masks for the head, torso, arms etc. If the move is particularly crazy then you may want to do masks for upper, lower arm and hands.
Thanks for the advice - I'm going to move onto mocha once I've got the hang of other techniques.
It seems I was doing it all wrong. The way I found that works is to track the object in the footage layer, using scale, rotation and position. Set track type to Transform and Edit the Target as being the solid layer for the mask. That way the solid layer moves with the object being tracked and there was no need to copy and paste or delete any of the trackers after.
I've a lot of roto ahead of me so I'm just learning as many different techniques as I can - some work better in different situations.