We can use a png image as the first screen of a video. Can flowplayer generate or create an image based on the video and use it as thumbnail image?
As far as I know, it can't. This is caused by the fact, that Flowplayer is a player. The better practice is to get the thumbnail in another way (maybe as described here in Flowplayer docs) and display it as splash image (described here in Flowplayer docs) or as first item of a playlist (described here in Flowplayer docs).