Add histogram stats for average QP per frame for VP8 (for sent video streams):

webrtc/video/send_statistics_proxy_unittest.cc

 /*
  *  Copyright (c) 2013 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 309 matching lines @@
   // No switch, stats not should be updated.
   statistics_proxy_->SetContentType(
       VideoEncoderConfig::ContentType::kRealtimeVideo);
   EXPECT_EQ(0, test::NumHistogramSamples("WebRTC.Video.InputWidthInPixels"));
 
   // Switch to screenshare, real-time stats should be updated.
   statistics_proxy_->SetContentType(VideoEncoderConfig::ContentType::kScreen);
   EXPECT_EQ(1, test::NumHistogramSamples("WebRTC.Video.InputWidthInPixels"));
 }
 
+TEST_F(SendStatisticsProxyTest, VerifyQpHistogramStats) {
+  test::ClearHistograms();
+  const int kMinRequiredSamples = 200;
+  const int kQpIdx0 = 21;
+  const int kQpIdx1 = 39;
+  EncodedImage encoded_image;
+
+  RTPVideoHeader rtp_video_header;
+  rtp_video_header.codec = kRtpVideoVp8;
+
+  for (int i = 0; i < kMinRequiredSamples; ++i) {
+    rtp_video_header.simulcastIdx = 0;
+    encoded_image.qp_ = kQpIdx0;
+    statistics_proxy_->OnSendEncodedImage(encoded_image, &rtp_video_header);
+    rtp_video_header.simulcastIdx = 1;
+    encoded_image.qp_ = kQpIdx1;
+    statistics_proxy_->OnSendEncodedImage(encoded_image, &rtp_video_header);
+  }
+  statistics_proxy_.reset();
+  EXPECT_EQ(2, test::NumHistogramSamples("WebRTC.Video.Encoded.Qp.Vp8"));
+  EXPECT_EQ(kQpIdx1, test::LastHistogramSample("WebRTC.Video.Encoded.Qp.Vp8"));

[stefan-webrtc, 2016/03/22 15:12:46]

Shouldn't this be the average of 21 and 39?

[åsapersson, 2016/03/22 15:29:46]

QP is stored per ssrc e.g.
two qp samples should be recorded (one for each stream): 
simulcast_idx: 0 -> ssrcs[0] average of 21.
simulcast_idx: 1 -> ssrcs[1] average of 39.

+}
+
 TEST_F(SendStatisticsProxyTest, NoSubstreams) {
   uint32_t excluded_ssrc =
       std::max(
           *std::max_element(config_.rtp.ssrcs.begin(), config_.rtp.ssrcs.end()),
           *std::max_element(config_.rtp.rtx.ssrcs.begin(),
                             config_.rtp.rtx.ssrcs.end())) +
       1;
   // From RtcpStatisticsCallback.
   RtcpStatistics rtcp_stats;
   RtcpStatisticsCallback* rtcp_callback = statistics_proxy_.get();
@@ skipping 313 matching lines @@
 
   EXPECT_EQ(1, test::NumHistogramSamples(
                    "WebRTC.Video.Screenshare.FecBitrateSentInKbps"));
   EXPECT_EQ(static_cast<int>((rtx_counters.fec.TotalBytes() * 2 * 8) /
                              metrics::kMinRunTimeInSeconds / 1000),
             test::LastHistogramSample(
                 "WebRTC.Video.Screenshare.FecBitrateSentInKbps"));
 }
 
 }  // namespace webrtc