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.
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.