Short description of error
When messing around with masks or doing anything with lots of subsequent operations that cause Blender to automaticaly re-render, sometimes Blender can't keep up and stalls out. I've waited 20 minutes sometimes and Blender just sits there frozen.
Exact steps for others to reproduce the error
- Set up compositing nodes involving, for example, an HD video clip, a mask, and a viewer node.
- Go to the UV/image editor, select the viewer node as input and switch to Mask mode,.
- Drag your mask points around, forcing Blender to re-render as you are dragging. Keep moving that mouse around and eventually Blender will freeze.