Change-Id: Ie26b6ca8de733a527f820b16148e7a2231073f0f

Calculate the difference variance between last source frame and
current source frame. The variance is calculated at 16x16 block
level. The variances are compared to several thresholds to decide
final partition sizes.

An adaptive strategy is implemented to decide using
SOURCE_VAR_BASED_PARTITION or FIXED_PARTITION based on motions
in the video. The switching test is done once every
search_type_check_frequency frames.

The selection of source_var_thresh needs to be investigated
further later.

RTC set Borg test showed 0.424% overall psnr gain, and 0.357%
ssim gain. For clips with large enough static area, the
encoding speedup is around 2% to 15%.

Change-Id: Id7d268f1d8cbca7fb8026aa4a53b3c77459dc156

Copy up to a certain bsize, otherwise set to a fixed bsize.
This helsp to reduce artifact near moving boundary caused by full partition
copy without checking motion of super-block.
This artifact can occur at speeds 3,4 in real-time mode.
Issue: https://code.google.com/p/webm/issues/detail?id=738.

Change-Id: I05812521fd38816a467f72eb6a951cae4c227931

Change-Id: I7b2b690d2d51d55daa642be4131e5febd78cbe0a

Change-Id: I75ad328c6d719df81cc24f3ae21c152af4ebdacc

Change-Id: I6371ef7301c6bc3138552bd349e9bd154dee3e08

This commit slightly increases the bit allocation for key frame. This
improves speed -5 coding performance by 2.77% with aq-mode=0 and by
2.78% with aq-mode=3.

Change-Id: Iaa3e777f80b9706306606af06e89852bac146659

Parameterize the frame level quantization index used in non-RD
coding flow with cbr.

Change-Id: I79cfbd9c32c0d0fc33ad720d2180432e910baf7a

This commit reduces the frequency of frames using finer quantizer
in non-RD coding flow, and slightly tune up the quantizer resolution
when used. It provides 1.7% compression gains in speed -5 at no speed
difference.

Change-Id: I430249a51260a841a0402666e5ec1566e4f7d5a6

The new tolerance is a little higher than before (especially
for kf/gf/arf) so this change gives an encode speed up
for some clips up for speeds 0-2.

Change-Id: I63f7d6c9cc11c7f58742f41e250dcd3eab1741eb

Change-Id: I434682bbd4cb2089cd213d77ed5a5e06256dc45d

This commit adjusted the speed steps in rt mode to make the steps
more evenly spaced on speed and quality, specifically:
1. Merged 3 and 4 into one single step 3 and removed confilicting
features.
2. Move 8, 7, 6, 5 to be 7, 6, 5, 4 repsectively.

Change-Id: I38d56d61531f3561d772aef953c411c8fb38c063

Change-Id: I7d9874da8ff78a2d7e0cf11073af9c30538bc9a6