benoit_labourdette Should it be possible for you to manage the creation of video vignettes without FFMPEG on server ? I guess the answer is no, but I ask ;-)
Maybe. Would you be creating all your own video preview images manually then, by taking a screenshot? To achieve something like this, I would need Files Gallery to "look" for a file for example _files_videofilename.jpg that matches the video name, that is hidden from the normal gallery. All in all, it's a clumsy process.
benoit_labourdette My web host (that is shared hosting) doesn't install FFMPEG on the server (I asked them and they don't have the intention to do it, I don't know why).
Probably because of the risks of cpu resources it could take on shared hosting. Creating a thumbnail is not such a huge task, but with FFMPEG, someone could start processing and resizing full movies from PHP, probably not something they want to risk on shared hosting.