Fire canplaythrough event at the proper time for audio/video

media/base/download_rate_monitor.h

+// Copyright (c) 2011 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_DOWNLOAD_RATE_MONITOR_H_
+#define MEDIA_BASE_DOWNLOAD_RATE_MONITOR_H_
+
+#include <deque>
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/time.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Measures download speed based on the rate at which a media file is buffering.
+// Signals when it believes the media file can be played back without needing to
+// pause to buffer.
+class MEDIA_EXPORT DownloadRateMonitor {
+ public:
+  explicit DownloadRateMonitor();

[scherkus (not reviewing), 2011/11/16 02:15:17]

nit: explicit isn't needed

+
+  // Begin measuring download rate. The monitor will run |canplaythrough_cb|
+  // when it believes the media can be played back without needing to pause to
+  // buffer. |media_bitrate| is the bitrate of the video.
+  void Start(const base::Closure& canplaythrough_cb, int media_bitrate);
+
+  // Notifies the monitor of the current number of bytes buffered by the media
+  // file at what timestamp. The monitor expects subsequent calls to
+  // SetBufferedBytes to have monotonically nondecreasing timestamps.
+  // Calls to the method are ignored if monitor has not been started or is
+  // stopped.
+  void SetBufferedBytes(int64 buffered_bytes, const base::Time& timestamp);
+
+  // Notifies the monitor when the media file has paused or continued
+  // downloading data.
+  void SetNetworkActivity(bool is_downloading_data);
+
+  // Sets the size of the media file in bytes.
+  void SetTotalBytes(int64 total_bytes) { total_bytes_ = total_bytes; }

[scherkus (not reviewing), 2011/11/16 02:15:17]

trivial setters/getters should be unix_hacker() style and typically you don't
even need comments as it's quite obvious what's going on

set_total_bytes()

+
+  // Sets whether the media file is a fully loaded source.
+  void SetLoaded(bool loaded) { loaded_ = loaded; }

[scherkus (not reviewing), 2011/11/16 02:15:17]

set_loaded()

+
+  // Stop monitoring download rate. This does not discard previously learned
+  // information, but it will no longer factor incoming information into its
+  // canplaythrough estimation.
+  void Stop();
+
+  // Resets monitor to uninitialized state.
+  void Reset();
+
+ private:
+  // Represents a point in time in which the media was buffering data.
+  struct BufferingPoint {
+    // The number of bytes buffered by the media player at |timestamp|.
+    int64 buffered_bytes;
+    // Time at which buffering measurement was taken.
+    base::Time timestamp;
+  };
+
+  // Represents a span of time in which the media was buffering data.
+  class Sample {
+   public:
+    explicit Sample();

[scherkus (not reviewing), 2011/11/16 02:15:17]

no explicit

+    Sample(const BufferingPoint& start, const BufferingPoint& end);
+
+    // Set the end point of the data sample.
+    void set_end(const BufferingPoint& new_end);
+
+    const BufferingPoint& start() const { return start_; }
+    const BufferingPoint& end() const { return end_; }
+
+    // Returns the bytes downloaded per second in this sample. Returns -1.0 if
+    // sample is invalid.
+    float bytes_per_second() const;
+
+    // Returns the seconds elapsed in this sample. Returns -1.0 if the sample
+    // has not begun yet.
+    float seconds_elapsed() const;
+
+    // Returns bytes downloaded in this sample. Returns -1.0 if the sample has
+    // not begun yet.
+    int64 bytes_downloaded() const;
+
+    // Returns true if Sample has not been initialized.
+    bool is_null() const;
+
+    // Resets the sample to an uninitialized state.
+    void Reset();
+
+    // Restarts the sample to begin its measurement at what was previously its
+    // end point.
+    void RestartAtEndBufferingPoint();
+
+   private:
+    BufferingPoint start_;
+    BufferingPoint end_;
+  };
+
+  int64 bytes_downloaded_in_window() const;
+  float seconds_elapsed_in_window() const;
+
+  // Updates window with latest sample if it is ready.
+  void UpdateSampleWindow();
+
+  // Returns an approximation of the current download rate in bytes per second.
+  // Returns -1.0 if unknown.
+  float ApproximateDownloadByteRate() const;
+
+  // Helper method that returns true if the monitor believes it should fire the
+  // |canplaythrough_cb_|.
+  bool ShouldNotifyCanPlayThrough();
+
+  // Examines the download rate and fires the |canplaythrough_cb_| callback if
+  // the monitor deems it the right time.
+  void NotifyCanPlayThroughIfNeeded();
+
+  // Callback to run when the monitor believes the media can play through
+  // without needing to pause to buffer.
+  base::Closure canplaythrough_cb_;
+
+  // Indicates whether the monitor has run the |canplaythrough_cb_|.
+  bool has_notified_can_play_through_;
+
+  // Measurements used to approximate download speed.
+  Sample current_sample_;
+  std::deque<Sample> sample_window_;
+
+  // True if actively downloading bytes, false otherwise.
+  bool is_downloading_data_;
+
+  // Total number of bytes in the media file, 0 if unknown or undefined.
+  int64 total_bytes_;
+
+  // Amount of bytes buffered.
+  int64 buffered_bytes_;
+
+  // True if the media file is a fully loaded source, e.g. file:// protocol.
+  bool loaded_;
+
+  // Bitrate of the media file, 0 if unknown.
+  int bitrate_;
+
+  // True if the monitor has not yet started or has been stopped, false
+  // otherwise.
+  bool stopped_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadRateMonitor);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_DOWNLOAD_RATE_MONITOR_H_