You have not provided nearly enough information for anyone to assist. We know that you are trying to freeze the mask for Roto-brush and it crashes, but we do not know anything else.
What version of After Effects you are using? Is it 12.2.1? 11.0.4?
What are your computer's specs? What processor? What Operating System? How much RAM? What video card? Etc.
Has this ever worked before? Is it just this one clip that it crashes on? Or does it crash anytime you use the Roto-brush on any type of footage?
It looks like your footage is an mp4. Is this using the H.264 codec? Try transcoding to a better post-production codec (like DNxHD or Quicktime with the Photo-JPEG codec) and see if you can get it to work that way.
version of After Effects: 184.108.40.206
computer's specs: HP i7-4770 CPU@3.40
OS: Windows 8.1 64 bits - Processor x64
Ram : 16,0 Go
Video card: GeForce GTX 660
The crash machine is the second time. Yes I use MP4. I Will change the codec.