Add QVGA to thresholds for initial quality.

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"
 
 namespace webrtc {
 
 namespace {
 static const int kMinFps = 5;
 // Threshold constant used until first downscale (to permit fast rampup).
 static const int kMeasureSecondsFastUpscale = 2;
 static const int kMeasureSecondsUpscale = 5;
 static const int kMeasureSecondsDownscale = 5;
 static const int kFramedropPercentThreshold = 60;
-static const int kHdResolutionThreshold = 700 * 500;
-static const int kHdBitrateThresholdKbps = 500;
 // Min width/height to downscale to, set to not go below QVGA, but with some
 // margin to permit "almost-QVGA" resolutions, such as QCIF.
 static const int kMinDownscaleDimension = 140;
 }  // namespace
 
 QualityScaler::QualityScaler()
     : low_qp_threshold_(-1), framerate_down_(false) {}
 
 void QualityScaler::Init(int low_qp_threshold,
                          int high_qp_threshold,
                          bool use_framerate_reduction,
                          int initial_bitrate_kbps,
                          int width,
                          int height,
                          int fps) {
   ClearSamples();
   low_qp_threshold_ = low_qp_threshold;
   high_qp_threshold_ = high_qp_threshold;
   use_framerate_reduction_ = use_framerate_reduction;
   downscale_shift_ = 0;
   // Use a faster window for upscaling initially (but be more graceful later).
   // This enables faster initial rampups without risking strong up-down
   // behavior later.
   measure_seconds_upscale_ = kMeasureSecondsFastUpscale;
   const int init_width = width;
   const int init_height = height;
-  // TODO(glaznev): Investigate using thresholds for other resolutions
-  // or threshold tables.
-  if (initial_bitrate_kbps > 0 &&
-      initial_bitrate_kbps < kHdBitrateThresholdKbps) {
-    // Start scaling to roughly VGA.
-    while (width * height > kHdResolutionThreshold) {
+  if (initial_bitrate_kbps > 0) {
+    // Resolutions a bit above their actual values to permit near-VGA and
+    // near-QVGA resolutions to use the same mechanism.
+    int init_num_pixels = width * height;
+    static const int kVgaBitrateThresholdKbps = 500;

[AlexG, 2016/04/18 20:30:03]

Why not to keep all these constants at the start where all constants are
declared.
Mixing constants declaration and code looks a little messy.

[pbos-webrtc, 2016/04/18 20:41:44]

Done.

+    static const int kVgaNumPixels = 700 * 500;  // 640x480
+    if (initial_bitrate_kbps < kVgaBitrateThresholdKbps)
+      init_num_pixels = kVgaNumPixels;
+    static const int kQvgaBitrateThresholdKbps = 250;
+    static const int kQvgaNumPixels = 400 * 300;  // 320x240
+    if (initial_bitrate_kbps < kQvgaBitrateThresholdKbps)
+      init_num_pixels = kQvgaNumPixels;
+    while (width * height > init_num_pixels) {
       ++downscale_shift_;
       width /= 2;
       height /= 2;
     }
   }
   UpdateTargetResolution(init_width, init_height);
   ReportFramerate(fps);
   target_framerate_ = -1;
 }
 
@@ skipping 112 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