Why does it say Im missing FFmpeg?
Gallery 3 attempts to use FFmpeg to examine uploaded movies. Without this, it can’t tell what type of movie you just uploaded. FFmpeg is used to extract a frame from your movie to use as a thumbnail and to find the dimensions of the video for playback. Currently only FLV and MP4 files are supported in Gallery 3. You must install FFmpeg on your system in order to be able to upload movies with ease. If you don’t have or can’t get FFmpeg to work on your server, there are the community contributed modules, noFFmpeg and Video Dimensions as options.