https://bugs.freedesktop.org/show_bug.cgi?id=97075
--- Comment #5 from Andy Furniss adf.lists@gmail.com --- Well his omx test is 6x slower as well without load (though the test vid is very short).
So I think in addition to to the vaapi issue he is seeing some prime+HD 7970M dpm problem.
Though maybe forcing CPUs to high and re-testing would help rule out cpufreq messing things up.