[Orphis]

H264 is lacking a lot of features (behind patents) that are essential to real-time communications. It's available, but by far, the worst offender for call quality. Modern call technology will want to use temporal and spatial scaling which are not available in the profiles supported by most H264 encoders and decoders.

Those tools are available for VP8 (temporal only), VP9 and AV1 and improve the quality of calls quite a lot when used right. I don't know about about the internals of H265 and H266 as those are also behind patents and no one wanted to touch them in the real-time conferencing space.