vp9-svc: Allow for nonzero motion on spatial reference.

For nonrd pickmode on a given spatial layer, the spatial
(golden) reference was always only using zeromv for prediction.
In this patch if the downsampling filter used for generating
the lower spatial layer is an averaging filter (nonzero phase),
we allow for subpel motion on the spatial (golden) reference to
compensate for the shift. This is done by forcing the testing of
nonzero motion mode to compensate for spatial downsampling shift.

Improvement for cases where the downsampling is averaging filter.
In the current code this is only done for generating
resolutions <= QVGA.

Improvement for avgPSNR/SSIM on RTC set for speed 7: ~1.2%.
Gain is larger (~2-3%) for VGA clips with 2 spatial layers.
~1% speed slowdown for 3 layer SVC on mac.

Change-Id: I9ec4fa20a38947934fc650594596c25280c3b289

diff --git a/vp9/encoder/vp9_pickmode.c b/vp9/encoder/vp9_pickmode.c
index 99776f1bd59da08910fcc20057aaf7edfab5fec2..198852d0eca300ac615f25ca6cd9bf2cf3db25cb 100644 (file)
--- a/vp9/encoder/vp9_pickmode.c
+++ b/vp9/encoder/vp9_pickmode.c
@@ -1498,6 +1498,9 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
   MV_REFERENCE_FRAME best_second_ref_frame = NONE;
   int comp_modes = 0;
   int num_inter_modes = (cpi->use_svc) ? RT_INTER_MODES_SVC : RT_INTER_MODES;
+  int flag_svc_subpel = 0;
+  int svc_mv_col = 0;
+  int svc_mv_row = 0;
 
   init_ref_frame_cost(cm, xd, ref_frame_cost);
 
@@ -1647,6 +1650,18 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
   if (cpi->use_svc || cpi->oxcf.speed <= 7 || bsize < BLOCK_32X32)
     x->sb_use_mv_part = 0;
 
+  // Set the flag_svc_subpel to 1 for SVC if the lower spatial layer used
+  // an averaging filter for downsampling (phase = 8). If so, we will test
+  // a nonzero motion mode on the spatial (goldeen) reference.
+  // The nonzero motion is half pixel shifted to left and top (-4, -4).
+  if (cpi->use_svc && cpi->svc.spatial_layer_id > 0 &&
+      svc_force_zero_mode[GOLDEN_FRAME - 1] &&
+      cpi->svc.downsample_filter_phase[cpi->svc.spatial_layer_id - 1] == 8) {
+    svc_mv_col = -4;
+    svc_mv_row = -4;
+    flag_svc_subpel = 1;
+  }
+
   for (idx = 0; idx < num_inter_modes + comp_modes; ++idx) {
     int rate_mv = 0;
     int mode_rd_thresh;
@@ -1660,6 +1675,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
     int inter_mv_mode = 0;
     int skip_this_mv = 0;
     int comp_pred = 0;
+    int force_gf_mv = 0;
     PREDICTION_MODE this_mode;
     second_ref_frame = NONE;
 
@@ -1680,6 +1696,19 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
       comp_pred = 1;
     }
 
+    if (flag_svc_subpel && ref_frame == GOLDEN_FRAME) {
+      force_gf_mv = 1;
+      // Only test mode if NEARESTMV/NEARMV is (svc_mv_col, svc_mv_row),
+      // otherwise set NEWMV to (svc_mv_col, svc_mv_row).
+      if (this_mode == NEWMV) {
+        frame_mv[this_mode][ref_frame].as_mv.col = svc_mv_col;
+        frame_mv[this_mode][ref_frame].as_mv.row = svc_mv_row;
+      } else if (frame_mv[this_mode][ref_frame].as_mv.col != svc_mv_col ||
+                 frame_mv[this_mode][ref_frame].as_mv.row != svc_mv_row) {
+        continue;
+      }
+    }
+
     if (comp_pred) {
       const struct segmentation *const seg = &cm->seg;
       if (!cpi->allow_comp_inter_inter) continue;
@@ -1737,7 +1766,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
     // Skip non-zeromv mode search for golden frame if force_skip_low_temp_var
     // is set. If nearestmv for golden frame is 0, zeromv mode will be skipped
     // later.
-    if (force_skip_low_temp_var && ref_frame == GOLDEN_FRAME &&
+    if (!force_gf_mv && force_skip_low_temp_var && ref_frame == GOLDEN_FRAME &&
         frame_mv[this_mode][ref_frame].as_int != 0) {
       continue;
     }
@@ -1751,7 +1780,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
     }
 
     if (cpi->use_svc) {
-      if (svc_force_zero_mode[ref_frame - 1] &&
+      if (!force_gf_mv && svc_force_zero_mode[ref_frame - 1] &&
           frame_mv[this_mode][ref_frame].as_int != 0)
         continue;
     }
@@ -1808,7 +1837,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
                              &rd_thresh_freq_fact[mode_index])))
       continue;
 
-    if (this_mode == NEWMV) {
+    if (this_mode == NEWMV && !force_gf_mv) {
       if (ref_frame > LAST_FRAME && !cpi->use_svc &&
           cpi->oxcf.rc_mode == VPX_CBR) {
         int tmp_sad;
@@ -1949,7 +1978,7 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x, TileDataEnc *tile_data,
     if ((this_mode == NEWMV || filter_ref == SWITCHABLE) &&
         pred_filter_search &&
         (ref_frame == LAST_FRAME ||
-         (ref_frame == GOLDEN_FRAME &&
+         (ref_frame == GOLDEN_FRAME && !force_gf_mv &&
           (cpi->use_svc || cpi->oxcf.rc_mode == VPX_VBR))) &&
         (((mi->mv[0].as_mv.row | mi->mv[0].as_mv.col) & 0x07) != 0)) {
       int pf_rate[3];