you want to have an flv file start buffering (without playing) or you want a swf file to start buffering (without playing) or both? if an flv, what are you using to display the flv?
as2 or as3?
I was planning on embeding an flv or f4v video file inside of a swf file. I was told this would be more widely compatible (please correct me if I'm wrong).
i've not heard of any servers failing to support flv mime types. but there may be some. if you have one, i'd be interested in hearing that.
f4v mime type is a different story. but i don't know any reason why anyone will select an f4v file type and then embed that in a swf timeline. that defeats the only advantages that f4v has over flv.