Created attachment 402305 [details] Screencast demonstrating bug https://blogs.gnome.org/shell-dev/2020/06/19/gnome-shell-ux-bigger-picture/ contains two videos. The first one doesn't play in Tech Preview (currently using 2.29.1) for mysterious reasons, but forget about it because this bug report is about the second video. The second video plays fine, but only once. Clicking the replay button does not work. Pausing and playing the video after it has completed for the first time fails. Note: to test, make sure you have org.freedesktop.Platform.openh264//2.0 installed from the gnome-nightly repo. The version installed from flathub will break Tech Preview.
These are VP8 videos, so no need to worry about openh264, for once...
Created attachment 419982 [details] screencast Works for me
Works for me now too.