Thank you for your answers.
@PhotoPhysicsGuy Could you give more details? I’m fine with semi automatic methods, I don’t care to help a bit the program, just want to spend 5mn per frame.
@bazza I tried it, but 1) it takes ages to compute it for a single frame 2) after 5mn… either it just stop with a message “Killed”, without any reasons, or it just crashes my computer. Even if it would have worked, I’m afraid its way to ressource costly: I would need minimum half a year just to process a 25mn video.