Very strange thing!

I'm using videoJS, a HTML5 video plugin for wordpress and I want to allow my users to upload a video file and then stream it.

When I'm on user blog and I put the tag with the URL [video mp4=""] it doesn't work but if I use the video tag with the URL [video mp4=""] it works!

I remember reading once that since the script is using a masked URL, the whole file is being "passed" through PHP which makes it slower and can cause problem, is this what is happening here?