Logging basic bad call detection

webrtc/video/bad_call_threshold.h

Index: webrtc/video/bad_call_threshold.h
diff --git a/webrtc/video/bad_call_threshold.h b/webrtc/video/bad_call_threshold.h
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+/*
+ *  Copyright (c) 2016 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.
+ */
+
+#ifndef WEBRTC_VIDEO_BAD_CALL_THRESHOLD_H_
+#define WEBRTC_VIDEO_BAD_CALL_THRESHOLD_H_
+
+#include <memory>
+
+namespace webrtc {
+
+class BadCallThreshold {

[palmkvist, 2016/11/15 15:01:01]

I am by the way rather unhappy with this name, so any ideas are welcome.

[sprang_webrtc, 2016/11/16 13:20:09]

Hm, dunno. How about QualityThreshold?

+ public:
+  BadCallThreshold(int threshold,
+                   int default_measurement,
+                   float fraction,
+                   int max_measurements);
+
+  enum BadCallState {
+    NEWLY_LOW,
+    STILL_LOW,
+    NEWLY_HIGH,
+    STILL_HIGH,
+  };

[sprang_webrtc, 2016/11/14 13:14:15]

Could you add a short comment explaining these?
Also, I'd prefer an enum class.

+
+  BadCallState AddMeasurement(int measurement);
+
+ private:
+  const std::unique_ptr<int[]> buffer_;

[sprang_webrtc, 2016/11/14 13:14:15]

Unless we want to be able to dynamically change the threshold at runtime, I
don't think we actually need to store the values. If you just have a ringbuffer
of states and a counter for each state you can add and subtract values without
looping.

[palmkvist, 2016/11/15 15:01:01]

We do need the values to calculate the variance though.
As for removing the loop, when we need to calculate the variance as well we get
the choice between linear time per measurement and accurate variance or an
imprecise variance (that I'm not entirely sure how it relates) in constant time.

(Also, is there a preexisting ringbuffer somewhere? A cursory search when I
first did this didn't find anything that seemed general purpose and reusable)

[sprang_webrtc, 2016/11/16 13:20:09]

True. Though I think just keeping a sum of squares is good enough. 
There is one in the rtc event log directory. Not sure why it's not in
webrtc/base... Otherwise maybe just use a std::deque?

+  const int max_measurements_;
+  float fraction_;
+  int threshold_;
+  int next_index_;
+  bool is_high_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_VIDEO_BAD_CALL_THRESHOLD_H_