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vp9: Disable re_encode_overshoot feature for speed >= 6.

For real-time screen content mode: for speed >= 6 disable
the re_encode_overshoot feature. This means for speed >= 6
the Q and rate control is reset on slide changes based on
the scene/slide detection and the current Q (and not on a
first pass encoded frame at current Q).

This reduces encode time on slide changes, but may be less
accurate in deciding when to reset/max-out the Q.

Change-Id: Id0fdcafd55bc43bd8b3afee211e524f37c8ddce6

--- a/vp9/encoder/vp9_encoder.c

+++ b/vp9/encoder/vp9_encoder.c

@@ -4052,6 +4052,18 @@

     vp9_svc_assert_constraints_pattern(cpi);

   }

+  if (!cpi->sf.re_encode_overshoot_rt &&

+      (cpi->rc.high_source_sad ||

+       (cpi->use_svc && cpi->svc.high_source_sad_superframe))) {

+    // Check if this high_source_sad (scene/slide change) frame should be

+    // encoded at high/max QP, and if so, set the q and adjust some rate

+    // control parameters.

+    if (vp9_encodedframe_overshoot(cpi, -1, &q)) {

+      vp9_set_quantizer(cm, q);

+      vp9_set_variance_partition_thresholds(cpi, q, 0);

+    }

+  }

+

   // Variance adaptive and in frame q adjustment experiments are mutually

   // exclusive.

   if (cpi->oxcf.aq_mode == VARIANCE_AQ) {

--- a/vp9/encoder/vp9_ratectrl.c

+++ b/vp9/encoder/vp9_ratectrl.c

@@ -2803,15 +2803,22 @@

 // Test if encoded frame will significantly overshoot the target bitrate, and

 // if so, set the QP, reset/adjust some rate control parameters, and return 1.

+// frame_size = -1 means frame has not been encoded.

 int vp9_encodedframe_overshoot(VP9_COMP *cpi, int frame_size, int *q) {

   VP9_COMMON *const cm = &cpi->common;

   RATE_CONTROL *const rc = &cpi->rc;

+  SPEED_FEATURES *const sf = &cpi->sf;

   int thresh_qp = 7 * (rc->worst_quality >> 3);

   int thresh_rate = rc->avg_frame_bandwidth << 3;

   // Lower rate threshold for video.

   if (cpi->oxcf.content != VP9E_CONTENT_SCREEN)

     thresh_rate = rc->avg_frame_bandwidth << 2;

-  if (cm->base_qindex < thresh_qp && frame_size > thresh_rate) {

+  // If this decision is not based on an encoded frame size but just on

+  // scene/slide change detection (i.e., re_encode_overshoot_rt = 0), adjust the

+  // qp_thresh and skip the (frame_size > thresh_rate) condition in this case.

+  if (!sf->re_encode_overshoot_rt) thresh_qp = rc->worst_quality >> 1;

+  if ((!sf->re_encode_overshoot_rt || frame_size > thresh_rate) &&

+      cm->base_qindex < thresh_qp) {

     double rate_correction_factor =

         cpi->rc.rate_correction_factors[INTER_NORMAL];

     const int target_size = cpi->rc.avg_frame_bandwidth;

@@ -2827,7 +2834,8 @@

     // and the encoded frame used alot of Intra modes, then force hybrid_intra

     // encoding for the re-encode on this scene change. hybrid_intra will

     // use rd-based intra mode selection for small blocks.

-    if (frame_size > (thresh_rate << 1) && cpi->svc.spatial_layer_id == 0) {

+    if (sf->re_encode_overshoot_rt && frame_size > (thresh_rate << 1) &&

+        cpi->svc.spatial_layer_id == 0) {

       MODE_INFO **mi = cm->mi_grid_visible;

       int sum_intra_usage = 0;

       int mi_row, mi_col;

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

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

@@ -581,6 +581,7 @@

   }

   if (speed >= 6) {

+    sf->re_encode_overshoot_rt = 0;

     if (cpi->oxcf.rc_mode == VPX_VBR && cpi->oxcf.lag_in_frames > 0) {

       sf->use_altref_onepass = 1;

       sf->use_compound_nonrd_pickmode = 1;