All video codecs are covered by patents. All the popular ones, maybe. But MPEG-1 is over twenty years old, so unless there is a submarine patent out there, all the patents on it have already expired. Likewise, most aspects of MPEG-2 should be freed up within a decade. Even H.264 will eventually be unencumbered, given enough time.
On2 had a pile of active patents covering VP3, which they granted irrevocable royalty-free licenses to when they abandoned it to become Theora.
Nobody's ever done codec development without either filing a ton of patents or at least publishing rigorous documentation to establish prior art (Dirac). Some of those patents may no longer be in force, but they still exist.