Update RateStatistics to handle too-little-data case.

webrtc/video/receive_statistics_proxy.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 229 matching lines @@
       RTC_NOTREACHED() << "Unexpected stream ssrc: " << ssrc;
     }
   }
 }
 
 void ReceiveStatisticsProxy::OnDecodedFrame() {
   uint64_t now = clock_->TimeInMilliseconds();
 
   rtc::CritScope lock(&crit_);
   decode_fps_estimator_.Update(1, now);
-  stats_.decode_frame_rate = decode_fps_estimator_.Rate(now);
+  stats_.decode_frame_rate = decode_fps_estimator_.Rate(now).value_or(1);

[stefan-webrtc, 2016/06/02 07:16:42]

I'm not convinced this is correct. What if there are no samples? Shouldn't the
reported framerate be zero in that case?

[sprang_webrtc, 2016/06/02 08:09:32]

Yeah, you're right. I'll change it to default zero.
Same below.

[stefan-webrtc, 2016/06/02 08:14:39]

So, will we now ever be able to measure 1 fps? :)

[sprang, 2016/06/02 09:00:51]

Not if the actual rate is <= 1 fps. But slightly more and we'll round down to 1
:)
Do you think we should extend the window size for this, to say 2s? I'm
hesitant...

[stefan-webrtc, 2016/06/02 09:05:51]

Not sure. I'm mostly thinking whether it would make sense to report 1 fps if we
have 1 sample within the 1 second window in the frame rate case? Maybe it
doesn't? Seems like the way this is now implemented means that we will report 0
fps if the framerate is exactly 1 fps, which seems wrong?

[sprang_webrtc, 2016/06/02 12:23:50]

Done. PTAL

 }
 
 void ReceiveStatisticsProxy::OnRenderedFrame(int width, int height) {
   RTC_DCHECK_GT(width, 0);
   RTC_DCHECK_GT(height, 0);
   uint64_t now = clock_->TimeInMilliseconds();
 
   rtc::CritScope lock(&crit_);
   renders_fps_estimator_.Update(1, now);
-  stats_.render_frame_rate = renders_fps_estimator_.Rate(now);
+  stats_.render_frame_rate = renders_fps_estimator_.Rate(now).value_or(1);
   render_width_counter_.Add(width);
   render_height_counter_.Add(height);
   render_fps_tracker_.AddSamples(1);
   render_pixel_tracker_.AddSamples(sqrt(width * height));
 }
 
 void ReceiveStatisticsProxy::OnSyncOffsetUpdated(int64_t sync_offset_ms) {
   rtc::CritScope lock(&crit_);
   sync_offset_counter_.Add(std::abs(sync_offset_ms));
   stats_.sync_offset_ms = sync_offset_ms;
@@ skipping 30 matching lines @@
   ++num_samples;
 }
 
 int ReceiveStatisticsProxy::SampleCounter::Avg(int min_required_samples) const {
   if (num_samples < min_required_samples || num_samples == 0)
     return -1;
   return sum / num_samples;
 }
 
 }  // namespace webrtc