This is a regression on master branch, resulting from commit 2e79d05e

When watching videos with mpv under wayland, and using mpv's native wayland output (i.e. mpv --vo=gpu --gpu-context=wayland <video_file> ), the video output sometimes freezes while the audio keeps playing. The freeze can be triggered most of the time by pausing and resuming the playback, or by seeking the video. Also sometimes it occurs at seemingly random times. The video can be un-frozen by toggling between windowed and fullscreen mode.

There's an old mpv bug report, that seems to be about the same issue, and was closed as a mutter regression. On that report, it was determined (and I have confirmed myself) that the bug appeared after this mpv commit, and therefore only occurs with mpv 0.28.0 and later.