This isn't a problem, and falls more on the side of creative thinking. There is a website that is kind of a cross between YouTube and MySpace. They let you do live video conferencing, plus upload photos, audio and videos. I uploaded a video the other day and waited for it to render. When I looked at the listing the thumbnail image was a frame from the middle of the movie. I sent a message to someone who works for the company and asked how it was chosen. He replied and told me that the frame used is the "very middle frame" (I expected the first frame). So how then to make sure the thumbnail frame is one of your choosing.
I see two methods that can be used. First method: Just grab a
frame from somewhere in the video and make sure you drop it in to be
the middle frame. Not the cleanest way to do it, but it only lasts
1/30 of a second. Depending on the composition of the video the frame
grab might not be that disruptive. Second method: Add or subtract frames. If the frame you
want to use is near the middle, add or subtract frames to the beginning and/or end
of the video so that the desired frame becomes the middle frame. This could easily be done by shortening or lengthening the titles and credits before resorting to doing the same to scenes.
But if the frame you want as the thumbnail frame is near the beginning or end of the movie, what can you do? It's one thing to add frames to the end of a movie to shift the positioning of a single frame. People can turn it off whenever they like. But it is quite another to add frames to the beginning of a movie, where the viewer has to get through those frames to get to the movie.
I was looking at this as a mathematical puzzle. But then considered the possibility that there was a right-brained, non-linear approach to it, as well. I suppose you could hang a lantern on it and make it part of a quirky, off the wall kind of cult movie. But I was also interested in hearing how other people would apply their ingenuity and creativity to a puzzle like this. Any takers?