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vp9: Use scene detection for CBR mode.

Use the scene detection for CBR mode, and use it to reset the
rate control if large source sad is detected and rate
correctioni fact/QP is at minimum state.

Avoids large frame sizes after big content change following
low content period.

Only affects CBR mode for 1 pass at speeds 5, 6, 7.
Change-Id: I56dd853478cd5849b32db776e9221e258998d874

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

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

@@ -3524,12 +3524,13 @@

   vp9_update_noise_estimate(cpi);

-  // Scene detection is used for VBR mode or screen-content case.

-  // Make sure compute_source_sad_onepass is set (which handles SVC case

-  // and dynamic resize).

+  // Scene detection is always used for VBR mode or screen-content case.

+  // For other cases (e.g., CBR mode) use it for 5 <= speed < 8 for now

+  // (need to check encoding time cost for doing this for speed 8).

   if (cpi->compute_source_sad_onepass &&

       (cpi->oxcf.rc_mode == VPX_VBR ||

-       cpi->oxcf.content == VP9E_CONTENT_SCREEN))

+       cpi->oxcf.content == VP9E_CONTENT_SCREEN ||

+       (cpi->oxcf.speed >= 5 && cpi->oxcf.speed < 8)))

     vp9_scene_detection_onepass(cpi);

   // For 1 pass CBR SVC, only ZEROMV is allowed for spatial reference frame

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

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

@@ -353,6 +353,7 @@

   rc->af_ratio_onepass_vbr = 10;

   rc->prev_avg_source_sad_lag = 0;

   rc->high_source_sad = 0;

+  rc->reset_high_source_sad = 0;

   rc->high_source_sad_lagindex = -1;

   rc->alt_ref_gf_group = 0;

   rc->fac_active_worst_inter = 150;

@@ -585,7 +586,7 @@

   // In CBR mode, this makes sure q is between oscillating Qs to prevent

   // resonance.

-  if (cpi->oxcf.rc_mode == VPX_CBR &&

+  if (cpi->oxcf.rc_mode == VPX_CBR && !cpi->rc.reset_high_source_sad &&

       (!cpi->oxcf.gf_cbr_boost_pct ||

        !(cpi->refresh_alt_ref_frame || cpi->refresh_golden_frame)) &&

       (cpi->rc.rc_1_frame * cpi->rc.rc_2_frame == -1) &&

@@ -679,7 +680,8 @@

   int active_worst_quality;

   int ambient_qp;

   unsigned int num_frames_weight_key = 5 * cpi->svc.number_temporal_layers;

-  if (cm->frame_type == KEY_FRAME) return rc->worst_quality;

+  if (cm->frame_type == KEY_FRAME || rc->reset_high_source_sad)

+    return rc->worst_quality;

   // For ambient_qp we use minimum of avg_frame_qindex[KEY_FRAME/INTER_FRAME]

   // for the first few frames following key frame. These are both initialized

   // to worst_quality and updated with (3/4, 1/4) average in postencode_update.

@@ -1464,6 +1466,7 @@

   if (oxcf->pass == 0) {

     if (cm->frame_type != KEY_FRAME) compute_frame_low_motion(cpi);

   }

+  if (cm->frame_type != KEY_FRAME) rc->reset_high_source_sad = 0;

 }

 void vp9_rc_postencode_update_drop_frame(VP9_COMP *cpi) {

@@ -2330,6 +2333,23 @@

           rc->avg_source_sad[lagframe_idx] = avg_sad;

         }

       }

+    }

+    // For CBR non-screen content mode, check if we should reset the rate

+    // control. Reset is done if high_source_sad is detected and the rate

+    // control is at very low QP with rate correction factor at min level.

+    if (cpi->oxcf.rc_mode == VPX_CBR &&

+        cpi->oxcf.content != VP9E_CONTENT_SCREEN && !cpi->use_svc) {

+      if (rc->high_source_sad && rc->last_q[INTER_FRAME] == rc->best_quality &&

+          rc->avg_frame_qindex[INTER_FRAME] < (rc->best_quality << 1) &&

+          rc->rate_correction_factors[INTER_NORMAL] == MIN_BPB_FACTOR) {

+        rc->rate_correction_factors[INTER_NORMAL] = 0.5;

+        rc->avg_frame_qindex[INTER_FRAME] = rc->worst_quality;

+        rc->buffer_level = rc->optimal_buffer_level;

+        rc->bits_off_target = rc->optimal_buffer_level;

+        rc->reset_high_source_sad = 1;

+      }

+      if (cm->frame_type != KEY_FRAME && rc->reset_high_source_sad)

+        rc->this_frame_target = rc->avg_frame_bandwidth;

     }

     // For VBR, under scene change/high content change, force golden refresh.

     if (cpi->oxcf.rc_mode == VPX_VBR && cm->frame_type != KEY_FRAME &&

--- a/vp9/encoder/vp9_ratectrl.h

+++ b/vp9/encoder/vp9_ratectrl.h

@@ -169,6 +169,7 @@

   int avg_frame_low_motion;

   int af_ratio_onepass_vbr;

   int force_qpmin;

+  int reset_high_source_sad;

 } RATE_CONTROL;

 struct VP9_COMP;