Make sure we observe enough frames before scaling.

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.
  */
 
@@ skipping 21 matching lines @@
 static const int kMeasureMs = 2000;
 static const float kSamplePeriodScaleFactor = 2.5;
 static const int kFramedropPercentThreshold = 60;
 // QP scaling threshold defaults:
 static const int kLowH264QpThreshold = 24;
 static const int kHighH264QpThreshold = 37;
 // QP is obtained from VP8-bitstream for HW, so the QP corresponds to the
 // bitstream range of [0, 127] and not the user-level range of [0,63].
 static const int kLowVp8QpThreshold = 29;
 static const int kHighVp8QpThreshold = 95;
+static const int kMinFramesNeededToScale = 2 * 30;
 
 static VideoEncoder::QpThresholds CodecTypeToDefaultThresholds(
     VideoCodecType codec_type) {
   int low = -1;
   int high = -1;
   switch (codec_type) {
     case kVideoCodecH264:
       low = kLowH264QpThreshold;
       high = kHighH264QpThreshold;
       break;
@@ skipping 83 matching lines @@
 void QualityScaler::ReportQP(int qp) {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
   framedrop_percent_.AddSample(0);
   average_qp_.AddSample(qp);
 }
 
 void QualityScaler::CheckQP() {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
   // Should be set through InitEncode -> Should be set by now.
   RTC_DCHECK_GE(thresholds_.low, 0);
+
+  // If we have not observed at least this many frames we can't
+  // make a good scaling decision.
+  if (framedrop_percent_.size() < kMinFramesNeededToScale)
+    return;
+
   // Check if we should scale down due to high frame drop.
   const rtc::Optional<int> drop_rate = framedrop_percent_.GetAverage();
   if (drop_rate && *drop_rate >= kFramedropPercentThreshold) {
     ReportQPHigh();
     return;
   }
 
   // Check if we should scale up or down based on QP.
   const rtc::Optional<int> avg_qp = average_qp_.GetAverage();
   if (avg_qp) {
@@ skipping 25 matching lines @@
     fast_rampup_ = false;
   }
 }
 
 void QualityScaler::ClearSamples() {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
   framedrop_percent_.Reset();
   average_qp_.Reset();
 }
 }  // namespace webrtc