I have this project where there are explosions happening in a mine field. To do this, I purchased the explosions pack from tube tape. My problem is, the explosion footage stops before it is over!!! They usually end the clip before it goes out of frame, like this:
How am I supposed to use this? You can't just animate the transparency at the end to fade it, because it looks unrealistic due to it being still at the end. If anyone could give me tips how to composite this into my shot that would help.
That's the limitation of free or almost free special effects footage. If they let the smoke go to where it's dissipated, then you'd have a hard edge on the smoke where it goes out of the frame. If they had shot it wide enough to give you the full effect, letting the smoke rise and dissipate, you couldn't use it in a tight shot. It's a trade off, suitable only for quick cuts type of usage.
My suggestion would be to do a cutaway to a different shot - maybe a closeup of the person's face who is in the mine field, or a detail which moves the scene along. There is no really good (realistic, that is) way to use a partial effect, other than cutting away before it becomes a still frame. You'll notice in their demo reel of explosions, the effects all fade out before the still frame - not at all realistic...