Here is a link to the video:
All auto colour/levels/contrast has been added, and this doesn't appear to help.
I recorded 16 videos this day, and edited them all the same way. Only about 1/4 are flickering, the rest are fine.
You probably just need to tweak the matte a bit more in Keylight. Make sure that you're using a garbage matte to cut out most of the screen, then make very sure that your matte is complete.