So it's funny you outlined exactly what I created 2 years ago. I have all the code for uploading videos or gifs, running them through a combination of Imagemagick and ffmpeg to generate mp4/webm videos and image spritesheets for mobile devices. The only hitch now is probably the big cost of running these libraries on elastic computing services. ffmpeg is a beast, and it'll probably cost quite a bit of money to handle all the transcoding.