The area of video coder development based on the MPEG, H.264 and HEVC standards in active one and the hundred or more companies involved implement their designs with a mix of open generally available algorithms as well as methods and technologies they consider proprietary and for which they have obtained patents.
One source of information on such patents and their relations to one another is MPEG-LA. Please note it is not affiliated in any way with the Moving Pictures Experts Group. Rather MPEG LA is a firm based in Denver, Colorado that licenses patent pools covering essential patents required for use of the MPEG-2, MPEG-4 Visual (Part 2), IEEE 1394, VC-1, ATSC and AVC/H.264 standards.
Its activities are the subject of a lot of criticism within the video coder developer community. So, the information on this site has to be taken with a grain of salt. However, despite that, it is one of the few resources I've found that has a database of patent activity in this area and their relations to one another.