@fugi maybe there's a bias introduced through your extended knowledge of h264 encoding parameters vs. your less-extended knowledge of h265 and av1 encoding parameters :3
@stellavie that's not the point here π and h265 can definitely be much smaller (factor 2-5x) for e.g. entertainment media at 1080p at the same quality (to my eyes).
also if you need to have differing choices for whatever reason consider that it may make sense to choose the more modern codec for lower-fidelity video, not the other way around, since newer codecs are harder to decode and might become unplayable at resolutions like 4k where h264 will still playback fine
@fugi it could also just be the quality of the drivers and actual hardware encoders used. i know that, for example, the AV1 encoder from amd is quite terrible :3