AV1 RT: Adjust thrs for var-based partition. Add TX size search

This increases threshold for 32x32->16x16 split and adds tx size search
for speed 6. Overall perf impact is very small, but I see good BDRate
gain (overall 4%, max 9%) for speed 6. For speed7 the speed up is 11%
with BDRate loss of 0.22%.

Change-Id: I70e385fd232765d3e5a5eb4ceecf4ee8ff0b0864

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index ce86f0d..103e053 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -681,9 +681,7 @@
     sf->mode_search_skip_flags |= FLAG_SKIP_INTRA_DIRMISMATCH;
     sf->use_real_time_ref_set = 1;
     sf->tx_type_search.prune_mode = PRUNE_2D_MORE;
-    // Can't use LARGEST TX mode with pre-calculated partition
-    // and disabled TX64
-    if (!cpi->oxcf.enable_tx64) sf->tx_size_search_level = 1;
+    sf->tx_size_search_level = 1;
     sf->use_comp_ref_nonrd = 0;
     sf->inter_mode_rd_model_estimation = 2;
     sf->cdef_pick_method = CDEF_PICK_FROM_Q;
@@ -706,7 +704,6 @@
     sf->mv.search_method = FAST_DIAMOND;
     sf->partition_search_type = VAR_BASED_PARTITION;
     sf->mode_search_skip_flags |= FLAG_SKIP_INTRA_DIRMISMATCH;
-    sf->tx_size_search_level = 1;
     sf->use_nonrd_pick_mode = 1;
     sf->use_comp_ref_nonrd = 0;
     sf->inter_mode_rd_model_estimation = 2;

av1/encoder/var_based_part.c

diff --git a/av1/encoder/var_based_part.c b/av1/encoder/var_based_part.c
index 39a8d28..59b8c7e 100644
--- a/av1/encoder/var_based_part.c
+++ b/av1/encoder/var_based_part.c
@@ -416,7 +416,7 @@
       if (last_qindex >= QINDEX_HIGH_THR) {
         threshold_base = (5 * threshold_base) >> 1;
         thresholds[1] = threshold_base >> 3;
-        thresholds[2] = threshold_base;
+        thresholds[2] = threshold_base << 2;
         thresholds[3] = threshold_base << 5;
       } else if (last_qindex < QINDEX_LOW_THR) {
         thresholds[1] = threshold_base >> 3;