were you using a cutom ROM like Gummy Charged?
what app specifically were you using to stream videos, as the standard video player app (and google videos app) should work just fine. do you install another video player app that is overriding it?
I am able to get HDMI on my phone (but I'm rooted and using HumbleComb 5.0).
also, are you using Go Launcher? sometimes the image would not appear when using Go Launcher.