vp9: Increase thr_var for 32x32 blocks in var-based partitioning.

For real-time mode, increase variance threshold for 32x32 blocks in
var-based partitioning for resolution >= 720p, so that it is more
likely to stay at 32x32 for high resolution which accelerates the
encoding speed with little/no PSNR drop.

PSNR effect on different speed settings:
speed 8 rtc: 0.02 overall PSNR drop, 0.285% SSIM drop
speed 7 rtc: 0.196% overall PSNR increase, 0.066% SSIM increase
speed 5 rtc_derf: no effect.

Speed up:
gips_motion_WHD, 1mbps: 2.5% faster on speed 7, 2.6% faster on speed8
gips_stat_WHD, 1mbps: 4.6% faster on speed 7, 5.6% faster on speed8

Change-Id: Ie7c33c4d2dd7d09294917e031357fc5476c3a4bb

1 files changed, 7 insertions, 5 deletions

diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index f66ed9ed3..50e11948f 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -503,16 +503,18 @@ static void set_vbp_thresholds(VP9_COMP *cpi, int64_t thresholds[], int q) {
       else if (noise_level < kLow)
         threshold_base = (7 * threshold_base) >> 3;
     }
+    thresholds[0] = threshold_base;
+    thresholds[2] = threshold_base << cpi->oxcf.speed;
     if (cm->width <= 352 && cm->height <= 288) {
       thresholds[0] = threshold_base >> 3;
       thresholds[1] = threshold_base >> 1;
       thresholds[2] = threshold_base << 3;
-    } else {
-      thresholds[0] = threshold_base;
+    } else if (cm->width < 1280 && cm->height < 720) {
       thresholds[1] = (5 * threshold_base) >> 2;
-      if (cm->width >= 1920 && cm->height >= 1080)
-        thresholds[1] = (7 * threshold_base) >> 2;
-      thresholds[2] = threshold_base << cpi->oxcf.speed;
+    } else if (cm->width < 1920 && cm->height < 1080) {
+      thresholds[1] = threshold_base << 1;
+    } else {
+      thresholds[1] = (5 * threshold_base) >> 1;
     }
   }
 }