Help Rendering/exporting in iMovie 11'

I don't need help actually doing the exporting it's just whenever my video is exported it flashes and by that I mean certain sections of the screen get distorted for a second, but it happens often.

Some back round info:

I am exporting xbox gameplay
I am exporting a .mp4 file to .mov
My original file is a .m2ts and i have to convert the file to .mp4
I have tried more then one way of exporting
It has not flashed before. But very rarely does that happen.

Any help would be greatly appreciated on how to stop this.