ROTOSCOPE crashes when I try to FREEZE

Rotobrush is a resource hog, and that is probably the problem. You are probably just running out of system resources. Here are a couple of suggestions.

I always pre-compose a shot that needs Rotobrush making sure to trim the layer first to only the frames that I need to clean up and making sure that all attributes are moved to the new comp, and the comp is trimmed to the layer length. If there are areas in the shot that would benefit from some masking or even some color correction to improve edge detection, I apply masks or color correction before pre-composing. When you open the Layer panel to work Rotobrush, you don't want to see any extra frames as you do with a trimmed layer. It is also a very good idea not to have any other layers in a comp that needs Rotobrush. If you are starting with a complex composition, Pre-compose twice. Name the first Pre-comp something like "Original Footage," don't open that pre-comp, then Pre-compose that layer again and name it something like Rotobrush, open that comp, and do the work.

If there are any problems with the shot that come up I'll split the shot before pre-composing so I end up with shots that are shorter. In your case, split the layer you need to rotoscope in half, pre-compose each half, then do the roto, then freeze each half. I almost never Rotobrush a shot (comp) that is longer than six or seven seconds, even if the shot is a lot longer. There is just too much risk of a problem with long shots.

I hope this helps.

Any time that Rotobrush takes longer than a few seconds to Freeze, I use the Composition /Pre-render menu to render and replace the comp in the project, then delete the Rotobrush comp to reduce the project file size and free up system resources. 

Rotobrush is a good tool for shots that are well shot with the post-production workflow in mind, but it isn't perfect, and it still needs a lot of work to be fully optimized. I almost always use a Rotobrushed layer as a track matte for the original footage because almost all footage that you use the tool on can use some masking and color correction before you begin to improve the edge contrast and limit the area that Rotobrush searches for edges. 

Hey RickMo,

Sorry about the issue. Which version of After Effects are you currently on? Does After Effects crash every time you edit a specific frame using Rotobrush? If so, could you please let us know what type of source file you are working with (Format, codec, frame rate, frame size)? If you are working with h.264 or HEVC media files, please try transcoding them to something like Prores 422 and let us know if you still see the issue.

Thanks,

Ishan