Flickering/stuttering Video screen

I have recently been composing some music for a short film and everything was going smoothly until a few days ago when the video screen became unstable. Now, instead of paying the footage smoothly when I press play on the session, it stutters and flickers. It is making it difficult to write to as it is very hard to get a feel for the film when it is flickering all the way through. The track is playing smoothly so it’s nothing to do with buffer sizes or anything. It’s just the video footage that is playing back really weird. Even when the session is stopped, whatever frame the video is on, it is flickering and not just frozen on that specific frame.

I’ve reset the video preferences in the device menu but it hasn’t helped. Has anyone experienced this before and is there something I can do to fix it?

It is on cubase essentials 4 on a 2013 macbook pro