https://bugs.freedesktop.org/show_bug.cgi?id=79862
--- Comment #5 from nucrap@hotmail.com --- It just happened again with the same video: http://www.youtube.com/watch?v=d-Cc6j2ZBwk in 360p, firefox.
I don't know if I use UVD, but I don't think so (I guess this would require hw accelaration through gstreamer, but I don't have the corresponding packages installed).