Video background make audio/video freeze when chroma keying

Hi,

When I chroma key video and add a video background, my composition's audio and video keep skipping and freezing. But when I put a still as the background, it flows smoothly. This happens both in FCP 7 and in AE. Why is this happening when video backgrounds?

Thanks,
MJ

Sounds like your hardware is struggling to playback that much stuff at once. What happens if you render it in FCP first? What are your hardware specs, drives, and what video codec are you using?