Hello, Nathanael !
Thank you for your detailed and useful answer.
I wonder why Photosynth’s developers did add this feature (i.e. ability to work from video) since – as you say – it has been suggested for so long… Anyway.
I already try extracting a number of pictures from a video, but I did it manually, I’ll have a look at the softs you mention, thank you.
Regarding your remarks (compression of the video and camera motion), I have the possibility to capture video with as much care as needed (turning around the object very slowly for example, trying to have the more “stable” video as possible..) and I use a GoPro camera (HD)… So I think I can try to minimize those problems… And since my internet connection is so bad, I have to compress the pictures extracted from the video myself, so to be able to upload many of them on Photosynth :(