[cd34]

Do you have access to the raw logs provided by apache?

If so, if those pages are not that active, maybe post the logs for anything referring to that .flv and the page and we might be able to figure out why it might not be working.

First test would be to disable the rules to see if it does work in all of the browsers, ensuring that the encoding is indeed correct. Once you've done that, reinstate the rules, see what breaks. Then, post the raw logs of the failed requests and perhaps we can see a pattern.