Two Pass VBR change

Further experiment with restriction of the Q range.

This uses the average non KF/GF/ARF quantizer,  instead
of just relying on the initial value. It is not such a strong constraint
but there may be a reduced risk of rate misses.

Change-Id: I424fe782a37a2f4e18c70805e240db55bfaa25ec
2 files changed