A repeated annoyance of some Windows Phone 7 owners is that when using A2DP sound over Bluetooth, this will be disabled when playing video.
Of course the reason for this is somewhat understandable â€“ when decoding video, transcoding sound to the A2DP audio codec takes processor cycles which then lead to sound dropping out or low frame rate for video.
If however you want to take your chances and have an Interop unlocked device or a device with a built-in registry editor like some LG ones, Fabcal has a simple registry edit which will fix the issue.
With your unlocked handset and WP7 root tools or other registry editor, edit:
Change dword value DisableA2DPPLayback from 1 to 0
Reboot immediately afterward and enjoy Bluetooth Stereo Audio playback while watching video.
Note that as the Bluetooth antenna is often the same as the WIFI antenna they can interfere, making the solution better for playing local content than streaming content from the internet.
Read more in this XDA-Dev thread for methods of editing your registry on Windows Phone 7.