I've been using Imagor and Imagorvideo for sometime now and am very happy with it, especially since I often work with video files that aren't known to me (e.g. UGC or remote files). In my use case this has replaced Thumbor and a whole bunch of shell scripts and various other glue to handle unknown files.
We've built something similar long time ago and ability to control filters from client (as they are part of URL) is very powerful. E.g. clients with different native resolution, or ah hoc overlays are all under the frontend control and nicely cachable.
I use this for web video thumbnail manipulation. Having on-the-fly control right from the URL gives more versatility e.g. seeking by percentage, skipping the black frames etc. And this is more well suited with cloud storages.