3 files changed, 29 insertions, 2 deletions

diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index 568314174..ce178af75 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -2197,7 +2197,7 @@ static void rd_auto_partition_range(VP9_COMP *cpi, const TileInfo *const tile,
   max_size = find_partition_size(max_size,
                                  row8x8_remaining, col8x8_remaining,
                                  &bh, &bw);
-  min_size = MIN(min_size, max_size);
+  min_size = MIN(cpi->sf.rd_auto_partition_min_limit, MIN(min_size, max_size));
 
   // When use_square_partition_only is true, make sure at least one square
   // partition is allowed by selecting the next smaller square size as
diff --git a/vp9/encoder/vp9_speed_features.c b/vp9/encoder/vp9_speed_features.c
index 372f1673d..fd763f4f3 100644
--- a/vp9/encoder/vp9_speed_features.c
+++ b/vp9/encoder/vp9_speed_features.c
@@ -72,6 +72,29 @@ static void set_good_speed_feature_framesize_dependent(VP9_COMMON *cm,
   }
 }
 
+// Sets a partition size down to which the auto partition code will always
+// search (can go lower), based on the image dimensions. The logic here
+// is that the extent to which ringing artefacts are offensive, depends
+// partly on the screen area that over which they propogate. Propogation is
+// limited by transform block size but the screen area take up by a given block
+// size will be larger for a small image format stretched to full screen.
+static BLOCK_SIZE set_partition_min_limit(VP9_COMP *cpi) {
+  VP9_COMMON *const cm = &cpi->common;
+  unsigned int screen_area = (cm->width * cm->height);
+
+  // Select block size based on image format size.
+  if (screen_area < 1280 * 720) {
+    // Formats smaller in area than 720P
+    return BLOCK_4X4;
+  } else if (screen_area < 1920 * 1080) {
+    // Format >= 720P and < 1080P
+    return BLOCK_8X8;
+  } else {
+    // Formats 1080P and up
+    return BLOCK_16X16;
+  }
+}
+
 static void set_good_speed_feature(VP9_COMP *cpi, VP9_COMMON *cm,
                                    SPEED_FEATURES *sf, int speed) {
   const int boosted = frame_is_boosted(cpi);
@@ -116,7 +139,7 @@ static void set_good_speed_feature(VP9_COMP *cpi, VP9_COMMON *cm,
     sf->disable_filter_search_var_thresh = 100;
     sf->comp_inter_joint_search_thresh = BLOCK_SIZES;
     sf->auto_min_max_partition_size = RELAXED_NEIGHBORING_MIN_MAX;
-
+    sf->rd_auto_partition_min_limit = set_partition_min_limit(cpi);
     sf->allow_partition_search_skip = 1;
   }
 
@@ -416,6 +439,7 @@ void vp9_set_speed_features_framesize_independent(VP9_COMP *cpi) {
   sf->less_rectangular_check = 0;
   sf->use_square_partition_only = 0;
   sf->auto_min_max_partition_size = NOT_IN_USE;
+  sf->rd_auto_partition_min_limit = BLOCK_4X4;
   sf->default_max_partition_size = BLOCK_64X64;
   sf->default_min_partition_size = BLOCK_4X4;
   sf->adjust_partitioning_from_last_frame = 0;
diff --git a/vp9/encoder/vp9_speed_features.h b/vp9/encoder/vp9_speed_features.h
index ec2560e90..7f2f68c64 100644
--- a/vp9/encoder/vp9_speed_features.h
+++ b/vp9/encoder/vp9_speed_features.h
@@ -271,6 +271,9 @@ typedef struct SPEED_FEATURES {
   // Sets min and max partition sizes for this 64x64 region based on the
   // same 64x64 in last encoded frame, and the left and above neighbor.
   AUTO_MIN_MAX_MODE auto_min_max_partition_size;
+  // Ensures the rd based auto partition search will always
+  // go down at least to the specified level.
+  BLOCK_SIZE rd_auto_partition_min_limit;
 
   // Min and max partition size we enable (block_size) as per auto
   // min max, but also used by adjust partitioning, and pick_partitioning.