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vp9: SVC: Force subpel search off under certain conditions.

For SVC 1 pass non-rd mode:
Force subpel seach off for SVC for non-reference frames
under motion threshold.

Add flag to svc context to indicate if the frame is not used
as a reference.

Little/no quaity loss, ~2% speedup.

Change-Id: Ic433c44b514d19d08b28f80ff05231dc943b28e9

--- a/vp9/encoder/vp9_pickmode.c

+++ b/vp9/encoder/vp9_pickmode.c

@@ -158,6 +158,7 @@

   const MvLimits tmp_mv_limits = x->mv_limits;

   int rv = 0;

   int cost_list[5];

+  int search_subpel = 1;

   const YV12_BUFFER_CONFIG *scaled_ref_frame =

       vp9_get_scaled_ref_frame(cpi, ref);

   if (scaled_ref_frame) {

@@ -210,7 +211,12 @@

   rv =

       !(RDCOST(x->rdmult, x->rddiv, (*rate_mv + rate_mode), 0) > best_rd_sofar);

-  if (rv) {

+  // For SVC on non-reference frame, avoid subpel for (0, 0) motion.

+  if (cpi->use_svc && cpi->svc.non_reference_frame) {

+    if (mvp_full.row == 0 && mvp_full.col == 0) search_subpel = 0;

+  }

+

+  if (rv && search_subpel) {

     const int subpel_force_stop = cpi->sf.mv.subpel_force_stop;

     cpi->find_fractional_mv_step(

         x, &tmp_mv->as_mv, &ref_mv, cpi->common.allow_high_precision_mv,

--- a/vp9/encoder/vp9_speed_features.c

+++ b/vp9/encoder/vp9_speed_features.c

@@ -534,7 +534,11 @@

     if (cpi->svc.temporal_layer_id > 0) {

       sf->adaptive_rd_thresh = 4;

       sf->limit_newmv_early_exit = 0;

-      sf->mv.subpel_force_stop = (cpi->svc.temporal_layer_id == 1) ? 1 : 2;

+      // Use 1/2-pel for non-reference frame.

+      if (cpi->svc.non_reference_frame)

+        sf->mv.subpel_force_stop = 2;

+      else

+        sf->mv.subpel_force_stop = 1;

       sf->base_mv_aggressive =

           (cpi->svc.temporal_layer_id == cpi->svc.number_temporal_layers - 1)

               ? 1

--- a/vp9/encoder/vp9_svc_layercontext.c

+++ b/vp9/encoder/vp9_svc_layercontext.c

@@ -36,6 +36,7 @@

   svc->scaled_temp_is_alloc = 0;

   svc->scaled_one_half = 0;

   svc->current_superframe = 0;

+  svc->non_reference_frame = 0;

   for (i = 0; i < REF_FRAMES; ++i) svc->ref_frame_index[i] = -1;

   for (sl = 0; sl < oxcf->ss_number_layers; ++sl) {

     svc->ext_frame_flags[sl] = 0;

@@ -675,6 +676,12 @@

         break;

       }

     }

+  }

+

+  cpi->svc.non_reference_frame = 0;

+  if (cpi->common.frame_type != KEY_FRAME && !cpi->ext_refresh_last_frame &&

+      !cpi->ext_refresh_golden_frame && !cpi->ext_refresh_alt_ref_frame) {

+    cpi->svc.non_reference_frame = 1;

   }

   if (vp9_set_size_literal(cpi, width, height) != 0)

--- a/vp9/encoder/vp9_svc_layercontext.h

+++ b/vp9/encoder/vp9_svc_layercontext.h

@@ -87,6 +87,7 @@

   int ref_frame_index[REF_FRAMES];

   int force_zero_mode_spatial_ref;

   int current_superframe;

+  int non_reference_frame;

   int use_base_mv;

   // Used to control the downscaling filter for source scaling, for 1 pass CBR.

   // downsample_filter_phase: = 0 will do sub-sampling (no weighted average),