Depending on the backend, it could just be a filesystem, like WAFL/OnTap or OneFS. The videos get stashed per owner ID, and a database on a different box keeps the meta data in sync, deleting videos that expire.
Coupled with something like Isilon's SmartLock (which, in compliance mode, keeps stuff from being deleted unless one logs on as console root), it would provide decent protection against changes/deletions, barring physical compromise.
There are a lot of ways (some good, many brain-dead) to store video. A NAS can be used, or some type of cluster with EMC VNX LUNs and another machine doing an object database manage things.