Rate control on static scenes plus Y2dc delta Q fix.
A problem can arise on static clips with force key frames where attempts to avoid popping lead to a progressive reduction in key frame Q that ultimately may lead to unexpected overspend against the rate target. The changes in this patch help to insure that in such clips the quality of the key frames across the clip is more uniform (rather than starting bad and getting better - especially at low target rates). This patch also includes a fix that removes a delta on the Y2DC when the baseline q index < 4 as this is no longer needed. There is also a fix to try and prevent repeat single step Q adjustment in the recode loop leading to lots of recodes, especially where the use of forced skips as part of segmentation has made the impact of Q on the number of bits generated much smaller. Patch 2: Amend "last_boosted_qindex" calculation for arf overlay frames. Change-Id: Ia1feeb79ed8ed014e4239994fcf5e58e68fd9459