#webkit (for #epiphany) needed a small patch (https://trac.webkit.org/changeset/273960/webkit) to leverage the #gstreamer work that accelerates #h264 on the #librem5 (https://social.librem.one/@agx/105799071793016596). Resource usage did drop but not as much as i'd expected so there's more debugging needed.
Situation improves further when bringing the #arm64 #pixman optimizations forward to #PureOS #Byzantium (https://gitlab.freedesktop.org/pixman/pixman/-/merge_requests/20) which were only in amber-phone and which everyone needs to pull since it's not merged in #pixman upstream.
Those running #PureOS #Byzantium can grab #gstreamer debs from https://source.puri.sm/guido.gunther/gst-plugins-bad1.0/pipelines/65100 - it's just a backport of the #gstreamer devs upstream work back to 1.18.3.