I have one video in my project.
It's an AVI with properties that AE say are 29.97 fps (those specs are right from the project panel.
Rotobrush says "Frame rate mismatch" For best results set the composition to 59.34 fps to match the layer source.
Can someone plesae explain the apparent "mismatch"?
29.97 frames per second is 59.94 fields per second for interlaced footage. You must be using interlaced footage. Rotoscoping, using the Roto Brush tool, and various other precision tasks benefit from working in a composition with a frame rate that matches the field rate of the footage item (i.e., doubling the frame rate within the composition).
There's a tutorial by John Dickinson linked to from here that explains more: "Frame rate"
I redid my original export (from Premiere) and switched to Progressive - and that solved the issue.
Checking your link too.