So the issue is simply that the pi's GL driver only goes up to 2.1, and/or that GTK doesn't accept GL<3.0 (my vague understanding of the graphics situation on the pi is that the GLES driver has (had?) rather better support than GL, but that Vulkan was the real focus of development efforts -- https://www.raspberrypi.com/news/vulkan-update-version-1-1-conformance-for-raspberry-pi-4/ has some more info on that).
@seb128 yes, the following command line plays (for at least 20 seconds -- I didn't watch the whole thing) happily under totem:
MESA_GL_ VERSION_ OVERRIDE= 3.3 totem big_buck_ bunny_720p_ surround. mp4
So the issue is simply that the pi's GL driver only goes up to 2.1, and/or that GTK doesn't accept GL<3.0 (my vague understanding of the graphics situation on the pi is that the GLES driver has (had?) rather better support than GL, but that Vulkan was the real focus of development efforts -- https:/ /www.raspberryp i.com/news/ vulkan- update- version- 1-1-conformance -for-raspberry- pi-4/ has some more info on that).