Ask HN: Multimedia content repository with API

This seems like a fairly easy product to find, but I have been struggling with this for 2 weeks and I have not found anything that fit our - very basic - needs.

Basically, we need to store multimedia assets (audio/video,images) in a repository. The content should be categorized by content type and tagged with different values, much like many stock photos sites do when searching for photos. This repository should also have an API, so that others services can query and retrieve these contents.

My first obvious choice was a CMS, but after reviewing a few of them, they all seem centered around the front-end part (themes, page layout, content editing, etc), with very little support/documentation for the backend (storage,API).

Any pointer is really appreciated.