I got the exact same issue after upgrading. Had to look for a long time before figuring what happened. The solution is in the comments in this post: https://bugs.archlinux.org/task/24381
It involves deleting $HOME/.gstreamer-0.10/registry*.bin (user files, safely deleted) which will be regenerated.
Hopefully, you'll get MP4/Quicktime support back in GStreamer apps (Totem/Miro...). It worked for me.