OK the Totem developers at GNOME Bugzilla say this is a packaging problem and that "Some libraries that the gst-libav package relies on are missing." If I try "apt-cache search gst-libav" I see this is "gstreamer1.0-libav", which is already installed.
I have followed their advice and filed a new bug for the gst-libav1.0 package: https://bugs.launchpad.net/ubuntu/+source/gst- libav1.0/+bug/1751769 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1751578 Title: Totem no longer plays MP4s, despite correct plugins installed To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/totem/+bug/1751578/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs