I have never worked with video files programmatically, and was wondering what is the recommended approach for generating the thumbnail for a given video file, considering the context is for a web application for building knowledge bases.
So far, what I have thought is to decode the video file, get a specific frame (i.e. frame at 50% of the total duration), and then get the bytes from that frame to generate a PNG image.
The trouble with picking a specific frame is that you can always miss and get a black frame from the middle of a transition (the worst video I had for this was a video of a nightclub, where only 1 in 5 frames or so actually had content, and the rest were either all-white from a strobe hitting the lens dead-on, or all black because the strobe was off).
A trick I've used in the past is to convert every frame in an N second window to PNG, and keep the largest resulting PNG as the thumbnail; a low-entropy frame (like all-black, or all-white) will be a small PNG, so this tends to result in a useful thumbnail, since it chooses the frame that's got least entropy - which is usually informational.
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