Last I checked[0] I think there were some remaining H.263 patents in the US, but they only covered some error correction or optional annex features.
Interestingly enough, there's some non-standard-essential patents still floating around out there. For example, Mediatek patented converting Sorenson Spark bitstreams for decoding with standards-compliant H.263 hardware decoders[1], and that patent is still live until later in this decade.
[0] I wrote a Sorenson-flavored H.263 decoder in Rust for integration into Ruffle.
[1] The invention is literally just truncation-with-saturation wrapped in a bunch of patent language. If you have the money to front a legal fight against them, feel free to get the patent invalidated. But I don't think it matters.
Interestingly enough, there's some non-standard-essential patents still floating around out there. For example, Mediatek patented converting Sorenson Spark bitstreams for decoding with standards-compliant H.263 hardware decoders[1], and that patent is still live until later in this decade.
[0] I wrote a Sorenson-flavored H.263 decoder in Rust for integration into Ruffle.
[1] The invention is literally just truncation-with-saturation wrapped in a bunch of patent language. If you have the money to front a legal fight against them, feel free to get the patent invalidated. But I don't think it matters.