A company called Sisvel is assembling a pool of patents claiming to cover the AV1 video codec <https://www.techdirt.com/articles/20200312/04075244087/former-refrigerator-manufacturer-says-companies-using-open-source-royalty-free-video-technology-must-pay-to-license-2000-patents.shtml>. They expect to eventually have an arsenal of about 2000 patents, for which they will demand licence fees. If you remember, AV1 was created precisely to avoid the patent morass that surrounds H.265 aka HEVC.