From 6581817991801224d5016c86115daf79e74bad85 Mon Sep 17 00:00:00 2001
From: Marco Paniconi <marpan@google.com>
Date: Tue, 5 Feb 2019 10:54:28 -0800
Subject: [PATCH] vp8: Limit Q change for screen content CBR mode

Add last_q[] to layer context, and add limit on
Q change from previous layer/frame. For now put
hard limit of 12 for decrease.

For 1 pass CBR sreen content mode.

Change-Id: Ifb972c9b6831440c80b1cb07a054c577ece930ec
---
 vp8/encoder/onyx_if.c  |  4 ++++
 vp8/encoder/onyx_int.h |  1 +
 vp8/encoder/ratectrl.c | 14 ++++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/vp8/encoder/onyx_if.c b/vp8/encoder/onyx_if.c
index 07be0d989..a30821ac1 100644
--- a/vp8/encoder/onyx_if.c
+++ b/vp8/encoder/onyx_if.c
@@ -218,6 +218,8 @@ static void save_layer_context(VP8_COMP *cpi) {
   lc->frames_since_last_drop_overshoot = cpi->frames_since_last_drop_overshoot;
   lc->force_maxqp = cpi->force_maxqp;
   lc->last_frame_percent_intra = cpi->last_frame_percent_intra;
+  lc->last_q[0] = cpi->last_q[0];
+  lc->last_q[1] = cpi->last_q[1];
 
   memcpy(lc->count_mb_ref_frame_usage, cpi->mb.count_mb_ref_frame_usage,
          sizeof(cpi->mb.count_mb_ref_frame_usage));
@@ -255,6 +257,8 @@ static void restore_layer_context(VP8_COMP *cpi, const int layer) {
   cpi->frames_since_last_drop_overshoot = lc->frames_since_last_drop_overshoot;
   cpi->force_maxqp = lc->force_maxqp;
   cpi->last_frame_percent_intra = lc->last_frame_percent_intra;
+  cpi->last_q[0] = lc->last_q[0];
+  cpi->last_q[1] = lc->last_q[1];
 
   memcpy(cpi->mb.count_mb_ref_frame_usage, lc->count_mb_ref_frame_usage,
          sizeof(cpi->mb.count_mb_ref_frame_usage));
diff --git a/vp8/encoder/onyx_int.h b/vp8/encoder/onyx_int.h
index 5189d4338..a4e3f2f79 100644
--- a/vp8/encoder/onyx_int.h
+++ b/vp8/encoder/onyx_int.h
@@ -257,6 +257,7 @@ typedef struct {
 
   int count_mb_ref_frame_usage[MAX_REF_FRAMES];
 
+  int last_q[2];
 } LAYER_CONTEXT;
 
 typedef struct VP8_COMP {
diff --git a/vp8/encoder/ratectrl.c b/vp8/encoder/ratectrl.c
index d7badeb5a..dbd76edad 100644
--- a/vp8/encoder/ratectrl.c
+++ b/vp8/encoder/ratectrl.c
@@ -1125,6 +1125,14 @@ void vp8_update_rate_correction_factors(VP8_COMP *cpi, int damp_var) {
   }
 }
 
+static int limit_q_cbr_inter(int last_q, int current_q) {
+  int limit_down = 12;
+  if (last_q - current_q > limit_down)
+    return (last_q - limit_down);
+  else
+    return current_q;
+}
+
 int vp8_regulate_q(VP8_COMP *cpi, int target_bits_per_frame) {
   int Q = cpi->active_worst_quality;
 
@@ -1264,6 +1272,12 @@ int vp8_regulate_q(VP8_COMP *cpi, int target_bits_per_frame) {
     }
   }
 
+  // Limit decrease in Q for 1 pass CBR screen content mode.
+  if (cpi->common.frame_type != KEY_FRAME && cpi->pass == 0 &&
+      cpi->oxcf.end_usage == USAGE_STREAM_FROM_SERVER &&
+      cpi->oxcf.screen_content_mode)
+    Q = limit_q_cbr_inter(cpi->last_q[1], Q);
+
   return Q;
 }
 
-- 
2.40.0