I recently had an issue displaying jQuery Media full-screen videos in Drupal 6. After a little research, reading some threads and some trial and error, I was able to successfully display videos in full-screen mode. The fix ended up being quite simple, but there didn't seem to be a lot of documentation so here it is.
My Situation:
This fix assumes that you you're using jQuery Media module and successfully playing the video through JW Player of similar.
The Quick Fix:
1. Go to: Administer > Configuration > jQuery Media
2. Select Advanced Settings
3. Add allowfullscreen:'true' in the PARAMS field
4. Save configuration
Assumption: Why This Works:
Placing allowfullscreen:'true' string in the PARAMS filed sends the string to the params for the embedded media which is set to false by default. Once set to true the player will play in full-screen mode if selected.
I hope this quick fix works for you and saves a little time and frustration. Happy Drupling!