hedney3 
Developer

I had the same issue with my Thunderbolt and found a free app in the market place called, Audio Manager. It is a volume control app and it will allow you to turn up the System Volume on your phone. After turning up the system volume (I turned mine up to 7) your video audio playback will be perfect. You can keep the app or uninstall it and the volume you turned up will remain the same. You will still have the original volume controls. It worked for me, I hope this helps you.
Gary

I could use some help picking a custom rom and learning how to flash it to my newly rooted tbolt. Any help would be greatly appreciated.