vp9: Speed 8: More aggresive golden skip for low res.

Add a new, more aggresive short circuit: short_circuit_low_temp_var = 3 to skip
golden of any mode when variance is lower than threshold for low res.
This change only affects speed = 8, low resolution.

Metrics for avgPSNR/SSIM on rtc_derf (low resolution) show loss of
0.27/0.31%.
On Nexus 6, the encoding time is reduced by ~2.3% on average across all
low-res clips.

Visually little change on rtc_derf clips.

Change-Id: Ia8f7366fc2d49181a96733a380b4dbd7390246ec

1 files changed, 5 insertions, 1 deletions

diff --git a/vp9/encoder/vp9_pickmode.c b/vp9/encoder/vp9_pickmode.c
index 2b7ddbcd9..8b84c3825 100644
--- a/vp9/encoder/vp9_pickmode.c
+++ b/vp9/encoder/vp9_pickmode.c
@@ -1490,6 +1490,10 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
   if (cpi->sf.short_circuit_low_temp_var) {
     force_skip_low_temp_var =
         get_force_skip_low_temp_var(&x->variance_low[0], mi_row, mi_col, bsize);
+    // In the most aggresive short circuit, skip golden in any mode
+    if (cpi->sf.short_circuit_low_temp_var == 3 && force_skip_low_temp_var) {
+      usable_ref_frame = LAST_FRAME;
+    }
   }
 
   if (!((cpi->ref_frame_flags & flag_list[GOLDEN_FRAME]) &&
@@ -1558,7 +1562,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
       continue;
     }
 
-    if (cpi->sf.short_circuit_low_temp_var == 2 && force_skip_low_temp_var &&
+    if (cpi->sf.short_circuit_low_temp_var >= 2 && force_skip_low_temp_var &&
         ref_frame == LAST_FRAME && this_mode == NEWMV) {
       continue;
     }