I don't know of any patents on the MPEG-4 Part 12 format. They might exist but I don't know of them. If you implement AVIF you'd have to pay whatever licenses m

I don't know of any patents on the MPEG-4 Part 12 format. They might exist but I don't know of them. If you implement AVIF you'd have to pay whatever licenses might exist over the format. If there's no licenses over the format, you pay nothing. If there are licenses but you're already distributing MPEG-4 video content, JPEG2000, or HEIF your licenses you'd pay for those would cover your use of AVIF in the MP4 container. So to my knowledge the ISO MP4 container doesn't require license fees so there's no real downside for using it as the container for AVIF.