Unify hardware and software QP thresholds.

webrtc/modules/video_coding/utility/quality_scaler.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #include "webrtc/modules/video_coding/utility/quality_scaler.h"
@@ skipping 12 matching lines @@
 static const int kMinDownscaleDimension = 140;
 // Initial resolutions corresponding to a bitrate. Aa bit above their actual
 // values to permit near-VGA and near-QVGA resolutions to use the same
 // mechanism.
 static const int kVgaBitrateThresholdKbps = 500;
 static const int kVgaNumPixels = 700 * 500;  // 640x480
 static const int kQvgaBitrateThresholdKbps = 250;
 static const int kQvgaNumPixels = 400 * 300;  // 320x240
 }  // namespace
 
+// QP thresholds are chosen to be high enough to be hit in practice when quality
+// is good, but also low enough to not cause a flip-flop behavior (e.g. going up
+// in resolution shouldn't give so bad quality that we should go back down).
+
+const int QualityScaler::kLowVp8QpThreshold = 29;
+const int QualityScaler::kBadVp8QpThreshold = 100;

[AlexG, 2016/05/11 17:13:48]

I want to keep "bad" threshold at 90 at least for HW codec. 720p encoding may
looks too blocky at QP = 90 and never downscale

[pbos-webrtc, 2016/05/11 17:19:26]

Are you certain that this doesn't flip-flop for either pretty-still video or
when moving around a bit?

+
+const int QualityScaler::kLowH264QpThreshold = 22;
+const int QualityScaler::kBadH264QpThreshold = 35;
+
 QualityScaler::QualityScaler() : low_qp_threshold_(-1) {}
 
 void QualityScaler::Init(int low_qp_threshold,
                          int high_qp_threshold,
                          int initial_bitrate_kbps,
                          int width,
                          int height,
                          int fps) {
   ClearSamples();
   low_qp_threshold_ = low_qp_threshold;
@@ skipping 118 matching lines @@
     downscale_shift_ = 0;
   if (!up) {
     // Hit first downscale, start using a slower threshold for going up.
     measure_seconds_upscale_ = kMeasureSecondsUpscale;
     UpdateSampleCounts();
   }
   ClearSamples();
 }
 
 }  // namespace webrtc