I experienced this issue last night. I have the DX, and also a BB Tour, my wife also has the Tour. She sent me a video in email shot from her phone last night I saved it to video folder (Using Droidmail and OI File Manager) but doesn't even show up in Gallery. When I use OI I can find the file and open it, but playback is jerky and it freezes after a few seconds. I can move the slider bar past that point and it will play then stick.
I played some more with trying to get it to work, I transferred using Bluetooth from my Tour which allowed it to be seen in Gallery, but playback still the same lag and stick. I made sure to try it after killing tasks but no difference. Videos that were taken with my BB that I copied over are doing the same thing, very laggy and play usually about halfway then stick, so transferring from computer doesn't work either. Any ideas anybody?
Just tried sending as mms instead of email. It plays, but with no sound. Tried taking new video with BB then mms to DX and same results.