I'm not sure if there is a way to control mod_deflate from .htaccess (at least, I have not found a way). The problem that you described was a similar problem that I ran into when I first started using vShare. I would have the following symptoms:

1. Video would start with audio only, picture would not move.
2. Video and audio would start, but the bar under the video would not move or did not load properly.
3. Video and audio would start fine (usually after reloading the page).

All of which were due to (for me) mod_deflate.