I mentioned this problem several times.
What surprises me is, that no one else suggested they had the same problem.
But not really surprised, as with forums generally, most members would probably raise a sweat, if they tried to raise the energy to reply. Then they complain that forums are not very active.
Anyhow, - for those of you who can read, but not type, - this problem does not usually occur if one goes to Gallery after the length boot, and videos are played straight off.
But if one uses a few other Apps. and come back to play a video, or App. with a video, the video stops but the audio runs. The message on the screen will be, "This is an audio file."
I tried a new video player, Mobo Player (better player), but when the standard player goes down, this one will also not function.
Just had a search on the Net about this problem, and it is apparent that every Android devices, except Archos 5 (I have one), experiences the same problem.
The android forums generally, all have extensive threads on the problem.
So, it is not your particular Streak, but an Android problem. Perhaps some new software version in the future may solve the problem.