go-camo was indeed originally intended to proxy only images, for two reasons: 1) the camo project it was inspired by only proxied images 2) my use-case at the time only required proxying of images
In my experience, video files are "usually" either linked (by url, no content warning), uploaded (service hosts it, so no content warning), or inlined from some hosting service (eg. youtube, vimeo; ssl provided by service). Video files are also generally much larger than image content.
Can you further describe your use-case/requirements for proxying video?