Added UMA metrics for MediaSourcePlayer and MediaCodecPlayer

media/base/android/media_statistics.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_
+#define MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_
+
+#include <stdint.h>
+#include "base/time/time.h"
+#include "media/base/demuxer_stream.h"
+#include "media/base/timestamp_constants.h"
+
+namespace media {
+
+// FrameStatistics struct deals with frames of one stream, i.e. either
+// audio or video.
+struct FrameStatistics {
+  // Audio: total number of frames that have been rendered.

[xhwang, 2015/10/01 21:58:58]

How about late frames, as described in l.24.

[Tima Vaisburd, 2015/10/02 00:44:32]

Late frames are also rendered. I'm not sure I got this remark.

+  // Video: total number of frames that were supposed to be rendered. Late video
+  //        frames might be skipped, but are counted here.
+  uint32_t total = 0;
+
+  // A number of late frames. Late frames are a subset of the total frames.
+  // Audio: The frame is late if it might cause an underrun, i.e. comes from
+  //        decoder when audio buffer is already depleted.
+  // Video: The frame is late if it missed its presentation time as determined
+  //        by PTS when it comes from decoder.  The rendering policy (i.e.
+  //        render or skip) does not affect this number.
+  uint32_t late = 0;
+
+  void Clear() { total = late = 0; }
+
+  // Adds a frame to |total|.
+  void AddFrame() { ++total; }

[xhwang, 2015/10/01 21:58:58]

To be accurate, all Add*() functions should really be Increment*().

[Tima Vaisburd, 2015/10/02 00:44:32]

Renamed to IncrementFrameCount() and IncrementLateFrameCount().

+
+  // Adds a frame to |late|. For each AddLateFrame() call there should be
+  // preceding AddFrame() call.
+  void AddLateFrame(base::TimeDelta /* delay */) { ++late; }

[xhwang, 2015/10/01 21:58:58]

Why do you still pass in |delay| here?

[Tima Vaisburd, 2015/10/02 00:44:32]

Sorry, removed.

+};
+
+// MediaStatistics class gathers and reports playback quality statistics to UMA.
+//
+// This class is not thread safe. The caller should guarantee that operations
+// on FrameStatistics objects does not happen during Start() and
+// StopAndReport(). The Start() and StopAndReport() methods need to be called
+// sequantially.
+
+class MediaStatistics {
+ public:
+  MediaStatistics();
+  ~MediaStatistics();
+
+  // Returns the frame statistics for audio frames.
+  FrameStatistics& audio_frames() { return audio_frames_; }

[xhwang, 2015/10/01 21:58:58]

I would recommend to be as clear as possible. audio_frame_stats() would be much
better in this case.

[Tima Vaisburd, 2015/10/02 00:44:32]

Done.

+
+  // Returns the frame statistics for video frames.
+  FrameStatistics& video_frames() { return video_frames_; }
+
+  // Starts gathering statistics. Can be called several times in the row, the
+  // latest call takes effect.
+  void Start(base::TimeDelta current_playback_time);
+
+  // Stops gathering statistics, calculate and report results. When called
+  // in a row only the firts call will take effect.
+  void StopAndReport(base::TimeDelta current_playback_time);
+
+  // Adds starvation event. Starvation happens when the player interrupts
+  // the regular playback and asks for more data.
+  void AddStarvation() { ++num_starvations_; }
+
+ private:
+  // Resets the data to the initial state.
+  void Clear();
+
+  // Calculates relative data based on total frame numbers and reports it and
+  // the duration to UMA.
+  void Report(base::TimeDelta duration);
+
+  base::TimeDelta start_time_ = kNoTimestamp();
+  FrameStatistics audio_frames_;
+  FrameStatistics video_frames_;
+  uint32_t num_starvations_ = 0;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_