Clamp number of downscales in QualityScaler.

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 42 matching lines @@
     if (initial_bitrate_kbps < kVgaBitrateThresholdKbps)
       init_num_pixels = kVgaNumPixels;
     if (initial_bitrate_kbps < kQvgaBitrateThresholdKbps)
       init_num_pixels = kQvgaNumPixels;
     while (width * height > init_num_pixels) {
       ++downscale_shift_;
       width /= 2;
       height /= 2;
     }
   }
+
+  // Zero out width/height so they can be checked against inside
+  // UpdateTargetResolution.
+  res_.width = res_.height = 0;
   UpdateTargetResolution(init_width, init_height);
   ReportFramerate(fps);
 }
 
 // Report framerate(fps) to estimate # of samples.
 void QualityScaler::ReportFramerate(int framerate) {
   framerate_ = framerate;
   UpdateSampleCounts();
 }
 
@@ skipping 51 matching lines @@
   scaled_frame_.set_ntp_time_ms(frame.ntp_time_ms());
   scaled_frame_.set_timestamp(frame.timestamp());
   scaled_frame_.set_render_time_ms(frame.render_time_ms());
   scaled_frame_.set_rotation(frame.rotation());
 
   return scaled_frame_;
 }
 
 void QualityScaler::UpdateTargetResolution(int frame_width, int frame_height) {
   assert(downscale_shift_ >= 0);
+  int shifts_performed = 0;
+  for (int shift = downscale_shift_;
+       shift > 0 && (frame_width / 2 >= kMinDownscaleDimension) &&
+       (frame_height / 2 >= kMinDownscaleDimension);
+       --shift, ++shifts_performed) {
+    frame_width /= 2;
+    frame_height /= 2;
+  }
+  // Clamp to number of shifts actually performed to not be stuck trying to
+  // scale way beyond QVGA.
+  downscale_shift_ = shifts_performed;
+  if (res_.width == frame_width && res_.height == frame_height) {
+    // No reset done/needed, using same resolution.
+    return;
+  }
   res_.width = frame_width;
   res_.height = frame_height;
-  for (int shift = downscale_shift_;
-       shift > 0 && (res_.width / 2 >= kMinDownscaleDimension) &&
-       (res_.height / 2 >= kMinDownscaleDimension);
-       --shift) {
-    res_.width /= 2;
-    res_.height /= 2;
-  }
+  ClearSamples();
 }
 
 void QualityScaler::ClearSamples() {
   framedrop_percent_.Reset();
   average_qp_downscale_.Reset();
   average_qp_upscale_.Reset();
 }
 
 void QualityScaler::UpdateSampleCounts() {
   num_samples_downscale_ = static_cast<size_t>(
       kMeasureSecondsDownscale * (framerate_ < kMinFps ? kMinFps : framerate_));
   num_samples_upscale_ = static_cast<size_t>(
       measure_seconds_upscale_ * (framerate_ < kMinFps ? kMinFps : framerate_));
 }
 
 void QualityScaler::AdjustScale(bool up) {
   downscale_shift_ += up ? -1 : 1;
   if (downscale_shift_ < 0)
     downscale_shift_ = 0;
   if (!up) {
-    // Hit first downscale, start using a slower threshold for going up.
+    // First downscale hit, start using a slower threshold for going up.
     measure_seconds_upscale_ = kMeasureSecondsUpscale;
     UpdateSampleCounts();
   }
-  ClearSamples();
 }
 
 }  // namespace webrtc