Drop frames until specified bitrate is achieved.

webrtc/video/vie_encoder.cc

Index: webrtc/video/vie_encoder.cc
diff --git a/webrtc/video/vie_encoder.cc b/webrtc/video/vie_encoder.cc
index f78633d532f438f809dce7453fb57accfeff0dd7..c407dcba6e9867ff5e761f332d2c72e15fc47519 100644
--- a/webrtc/video/vie_encoder.cc
+++ b/webrtc/video/vie_encoder.cc
@@ -55,6 +55,17 @@ CpuOveruseOptions GetCpuOveruseOptions(bool full_overuse_time) {
   return options;
 }
 
+int MaximumFrameSizeForBitrate(int kbps) {
+  if (kbps > 0) {
+    if (kbps < 300 /* qvga */) {
+      return 320 * 240;
+    } else if (kbps < 500 /* vga */) {
+      return 640 * 480;
+    }
+  }
+  return std::numeric_limits<int>::max();
+}
+
 }  //  namespace
 
 class ViEEncoder::ConfigureEncoderTask : public rtc::QueuedTask {
@@ -441,6 +452,8 @@ void ViEEncoder::ReconfigureEncoder() {
 
   const auto scaling_settings = settings_.encoder->GetScalingSettings();
   if (scaling_enabled_ && scaling_settings.enabled) {
+    // Drop frames and scale down until desired quality is achieved.
+    initial_rampup_ = true;
     if (scaling_settings.thresholds) {
       quality_scaler_.reset(
           new QualityScaler(this, *(scaling_settings.thresholds)));
@@ -560,6 +573,15 @@ void ViEEncoder::EncodeVideoFrame(const VideoFrame& video_frame,
   last_frame_height_ = video_frame.height();
   last_frame_width_ = video_frame.width();
 
+  int expected_pixel_count =
+      MaximumFrameSizeForBitrate(encoder_start_bitrate_bps_ / 1000);
+  if (initial_rampup_ && video_frame.size() > expected_pixel_count) {
+    LOG(LS_INFO) << "Dropping frame. Too large for target bitrate.";
+    ScaleDown(kQuality);
+    return;
+  }
+  initial_rampup_ = false;
+
   TRACE_EVENT_ASYNC_STEP0("webrtc", "Video", video_frame.render_time_ms(),
                           "Encode");
 
@@ -725,7 +747,7 @@ void ViEEncoder::ScaleDown(ScaleReason reason) {
   LOG(LS_INFO) << "Scaling down resolution.";
   for (size_t i = 0; i < kScaleReasonSize; ++i) {
     LOG(LS_INFO) << "Scaled " << scale_counter_[i]
-                 << " times for reason: " << (i ? "quality" : "cpu");
+                 << " times for reason: " << (i ? "cpu" : "quality");
   }
 }