Shobe,

This could be for a number of reasons. My guess is that you're rending with a codec that utilizes either high compression or a low bitrate. This will cause the images to be blocky or chunky in appearance. To resolve this, make a custom template with higher quality settings when you save/render your videos. If you don't know how this works, write back here and I'd be glad to walk you through the process.

Hope this helps,
Nick LaMartina