https://bugs.freedesktop.org/show_bug.cgi?id=98005
--- Comment #36 from Andy Furniss adf.lists@gmail.com --- It seems this is a dual instance issue, as it doesn't happen with it disabled.
It doesn't seem to happen at normal bitrates, but at high bits per picture, say 25 fps 100mbit, there is a big difference between gop 30 and 300.
I also notice that the encode time raises for the higher gop.