Improve two pass VBR accuracy.
Adjustments to the GF interval choice and minimum boost. Adjustment to the calculation of 2 pass worst q. Compared to 09/29 head there is metrics hit on derf of (-0.123%,-0.191%) Compared to the September 29 head and a baseline on September 18 baseline the accuracy of the VBR rate control measured on the derf set is as follows:- Mean error % / Mean abs(error %) Sept 18 baseline (-7.0% / 14.76%) Sept 29 head (-15.7%, 19.8%) This check in (-1.5% / 14.4%) The mean undershoot is reduced slightly but the worst case overshoot on e.g. harbour/highway is increased. This will be addressed in a later patch. Change-Id: Iffd9b0ab7432a131c98fbaaa82d1e5b40be72b58