Visit https://speedqueen.com/ in Ephy Tech Preview. Note the video banner at the top of the page stutters. It shouldn't stutter. Might be related to bug #224689, or maybe not.
It stutters even when loaded directly: https://speedqueen.com/wp-content/uploads/2021/10/Website-Intro-15-sec-Compressed-2.mp4 And it stutters even when played with totem. So likely a GStreamer-level problem.
*** This bug has been marked as a duplicate of bug 234666 ***
https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/946