No HTML5, no skin and only audio with firefox, only loading bar with chrome

I'm trying to use videojs for a html5 video with fallback to flash for those browser that can't play html5.
I tried in two mode: with Video module setted to display html5 with videojs and without video module, displaying the file field directly with videojs and in both cases:

- Whit firefox HTML5 doesn't work (but the demo.html page of videojs works) and i see the flash player, I hear audio but I can't see video.
- Whit chrome i see the html5 skin and loading icon but video and audio don't work.

Maybe an incompatibility issue between Video, VideoJS, Media, Flowplayer?
There's a suggested way to retry step by step to find what's going wrong?

Thanks