Thumbnail API

[evillemez]

Automatic thumbnails are hard, and inconsistent at best. We can autogenerate (bad) thumbnails, which we currently do - but it would be best to allow clients to create specific thumbnails at a given time. We could add an API for this in the TranscodingBundle.

This API could accept a file upload (image), and set/transcode it. It could also accept a timecode for video resources, and schedule the backend transcoding to generate the thumbnails automatically.

While this is a very specific use-case, this wouldn't be a bad approach because it is too common to ignore. Ultimately the purpose of the Media API is to provide useful search/discovery, and visually representing the search results is a key part of that.