Fire canplaythrough event at the proper time for audio/video

In this CL, the browser fires the canplaythrough event based on an
approximation of the download speed of the media instead of firing the
event right away.

BUG=73609
TEST=NONE

Review URL: http://codereview.chromium.org/8399023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@110733 0039d316-1c4b-4281-b951-d872f2087c98

14 files changed, 648 insertions, 20 deletions

diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index d6013ff..a75f248 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -57,6 +57,10 @@ class MEDIA_EXPORT Demuxer
   // Returns the starting time for the media file.
   virtual base::TimeDelta GetStartTime() const = 0;
 
+  // Returns the content bitrate. May be obtained from container or
+  // approximated. Returns 0 if it is unknown.
+  virtual int GetBitrate() = 0;
+
  protected:
   Demuxer();
   FilterHost* host() { return host_; }
diff --git a/media/base/download_rate_monitor.cc b/media/base/download_rate_monitor.cc
new file mode 100644
index 0000000..863967c
--- /dev/null
+++ b/media/base/download_rate_monitor.cc
@@ -0,0 +1,250 @@
+// 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.
+
+#include "media/base/download_rate_monitor.h"
+
+#include "base/bind.h"
+#include "base/time.h"
+
+namespace media {
+
+// Number of samples to use to collect and average for each measurement of
+// download rate.
+static const size_t kNumberOfSamples = 5;
+
+// Minimum number of seconds represented in a sample period.
+static const float kSamplePeriod = 1.0;
+
+DownloadRateMonitor::Sample::Sample() {
+  Reset();
+}
+
+DownloadRateMonitor::Sample::~Sample() { }
+
+DownloadRateMonitor::Sample::Sample(
+    const BufferingPoint& start, const BufferingPoint& end) {
+  Reset();
+  start_ = start;
+  set_end(end);
+}
+
+void DownloadRateMonitor::Sample::set_end(const BufferingPoint& new_end) {
+  DCHECK(!start_.timestamp.is_null());
+  DCHECK(new_end.buffered_bytes >= start_.buffered_bytes);
+  DCHECK(new_end.timestamp >= start_.timestamp);
+  end_ = new_end;
+}
+
+float DownloadRateMonitor::Sample::bytes_per_second() const {
+  if (seconds_elapsed() > 0.0 && bytes_downloaded() >= 0)
+    return bytes_downloaded() / seconds_elapsed();
+  return -1.0;
+}
+
+float DownloadRateMonitor::Sample::seconds_elapsed() const {
+  if (start_.timestamp.is_null() || end_.timestamp.is_null())
+    return -1.0;
+  return (end_.timestamp - start_.timestamp).InSecondsF();
+}
+
+int64 DownloadRateMonitor::Sample::bytes_downloaded() const {
+  if (start_.timestamp.is_null() || end_.timestamp.is_null())
+    return -1.0;
+  return end_.buffered_bytes - start_.buffered_bytes;
+}
+
+bool DownloadRateMonitor::Sample::is_null() const {
+  return start_.timestamp.is_null() && end_.timestamp.is_null();
+}
+
+void DownloadRateMonitor::Sample::Reset() {
+  start_ = BufferingPoint();
+  end_ = BufferingPoint();
+}
+
+void DownloadRateMonitor::Sample::RestartAtEndBufferingPoint() {
+  start_ = end_;
+  end_ = BufferingPoint();
+}
+
+DownloadRateMonitor::DownloadRateMonitor() {
+  Reset();
+}
+
+void DownloadRateMonitor::Start(
+    const base::Closure& canplaythrough_cb, int media_bitrate) {
+  DCHECK(stopped_);
+  canplaythrough_cb_ = canplaythrough_cb;
+  stopped_ = false;
+  bitrate_ = media_bitrate;
+  current_sample_.Reset();
+  buffered_bytes_ = 0;
+
+  NotifyCanPlayThroughIfNeeded();
+}
+
+void DownloadRateMonitor::SetBufferedBytes(
+    int64 buffered_bytes, const base::Time& timestamp) {
+  if (stopped_)
+    return;
+
+  is_downloading_data_ = true;
+
+  // Check monotonically nondecreasing constraint.
+  base::Time previous_time;
+  if (!current_sample_.is_null())
+    previous_time = current_sample_.end().timestamp;
+  else if (!sample_window_.empty())
+    previous_time = sample_window_.back().end().timestamp;
+
+  // If we go backward in time, dismiss the sample.
+  if (!previous_time.is_null() && timestamp < previous_time)
+    return;
+
+  // If the buffer level has dropped, invalidate current sample.
+  if (buffered_bytes < buffered_bytes_)
+    current_sample_.Reset();
+  buffered_bytes_ = buffered_bytes;
+
+  BufferingPoint latest_point = { buffered_bytes, timestamp };
+  if (current_sample_.is_null())
+    current_sample_ = Sample(latest_point, latest_point);
+  else
+    current_sample_.set_end(latest_point);
+
+  UpdateSampleWindow();
+  NotifyCanPlayThroughIfNeeded();
+}
+
+void DownloadRateMonitor::SetNetworkActivity(bool is_downloading_data) {
+  if (is_downloading_data == is_downloading_data_)
+    return;
+  // Invalidate the current sample if downloading is going from start to stopped
+  // or vice versa.
+  current_sample_.Reset();
+  is_downloading_data_ = is_downloading_data;
+}
+
+void DownloadRateMonitor::Stop() {
+  stopped_ = true;
+  current_sample_.Reset();
+  buffered_bytes_ = 0;
+}
+
+void DownloadRateMonitor::Reset() {
+  canplaythrough_cb_.Reset();
+  has_notified_can_play_through_ = false;
+  current_sample_.Reset();
+  sample_window_.clear();
+  is_downloading_data_ = false;
+  total_bytes_ = -1;
+  buffered_bytes_ = 0;
+  loaded_ = false;
+  bitrate_ = 0;
+  stopped_ = true;
+}
+
+DownloadRateMonitor::~DownloadRateMonitor() { }
+
+int64 DownloadRateMonitor::bytes_downloaded_in_window() const {
+  // There are max |kNumberOfSamples| so we might as well recompute each time.
+  int64 total = 0;
+  for (size_t i = 0; i < sample_window_.size(); ++i)
+    total += sample_window_[i].bytes_downloaded();
+  return total;
+}
+
+float DownloadRateMonitor::seconds_elapsed_in_window() const {
+  // There are max |kNumberOfSamples| so we might as well recompute each time.
+  float total = 0.0;
+  for (size_t i = 0; i < sample_window_.size(); ++i)
+    total += sample_window_[i].seconds_elapsed();
+  return total;
+}
+
+void DownloadRateMonitor::UpdateSampleWindow() {
+  if (current_sample_.seconds_elapsed() < kSamplePeriod)
+    return;
+
+  // Add latest sample and remove oldest sample.
+  sample_window_.push_back(current_sample_);
+  if (sample_window_.size() > kNumberOfSamples)
+    sample_window_.pop_front();
+
+  // Prepare for next measurement.
+  current_sample_.RestartAtEndBufferingPoint();
+}
+
+float DownloadRateMonitor::ApproximateDownloadByteRate() const {
+  // Compute and return the average download byte rate from within the sample
+  // window.
+  // NOTE: In the unlikely case where the data is arriving really bursty-ly,
+  // say getting a big chunk of data every 5 seconds, then with this
+  // implementation it will take 25 seconds until bitrate is calculated.
+  if (sample_window_.size() >= kNumberOfSamples &&
+      seconds_elapsed_in_window() > 0.0) {
+    return bytes_downloaded_in_window() / seconds_elapsed_in_window();
+  }
+
+  // Could not determine approximate download byte rate.
+  return -1.0;
+}
+
+bool DownloadRateMonitor::ShouldNotifyCanPlayThrough() {
+  if (stopped_)
+    return false;
+
+  // Only notify CanPlayThrough once for now.
+  if (has_notified_can_play_through_)
+    return false;
+
+  // If the media is from a local file (|loaded_|) or if all bytes are
+  // buffered, fire CanPlayThrough.
+  if (loaded_ || buffered_bytes_ == total_bytes_)
+    return true;
+
+  // Cannot approximate when the media can play through if bitrate is unknown.
+  if (bitrate_ <= 0)
+    return false;
+
+  float bytes_needed_per_second = bitrate_ / 8;
+  float download_rate = ApproximateDownloadByteRate();
+
+  // If we are downloading at or faster than the media's bitrate, then we can
+  // play through to the end of the media without stopping to buffer.
+  if (download_rate > 0)
+    return download_rate >= bytes_needed_per_second;
+
+  // If download rate is unknown, it may be because the media is being
+  // downloaded so fast that it cannot collect an adequate number of samples
+  // before the download gets deferred.
+  //
+  // To catch this case, we also look at how much data is being downloaded
+  // immediately after the download begins.
+  if (sample_window_.size() < kNumberOfSamples) {
+    int64 bytes_downloaded_since_start =
+        bytes_downloaded_in_window() + current_sample_.bytes_downloaded();
+    float seconds_elapsed_since_start =
+        seconds_elapsed_in_window() + current_sample_.seconds_elapsed();
+
+    // If we download 4 seconds of data in less than 2 seconds of time, we're
+    // probably downloading at a fast enough rate that we can play through.
+    // This is an arbitrary metric that will likely need tweaking.
+    if (seconds_elapsed_since_start < 2.0 &&
+        bytes_downloaded_since_start > 4.0 * bytes_needed_per_second) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void DownloadRateMonitor::NotifyCanPlayThroughIfNeeded() {
+  if (ShouldNotifyCanPlayThrough() && !canplaythrough_cb_.is_null()) {
+    canplaythrough_cb_.Run();
+    has_notified_can_play_through_ = true;
+  }
+}
+
+}  // namespace media
diff --git a/media/base/download_rate_monitor.h b/media/base/download_rate_monitor.h
new file mode 100644
index 0000000..ac88f7f
--- /dev/null
+++ b/media/base/download_rate_monitor.h
@@ -0,0 +1,155 @@
+// 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:
+  DownloadRateMonitor();
+  ~DownloadRateMonitor();
+
+  // 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);
+
+  void set_total_bytes(int64 total_bytes) { total_bytes_ = total_bytes; }
+
+  void set_loaded(bool loaded) { loaded_ = 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:
+    Sample();
+    Sample(const BufferingPoint& start, const BufferingPoint& end);
+    ~Sample();
+
+    // 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_
diff --git a/media/base/download_rate_monitor_unittest.cc b/media/base/download_rate_monitor_unittest.cc
new file mode 100644
index 0000000..787a5b4
--- /dev/null
+++ b/media/base/download_rate_monitor_unittest.cc
@@ -0,0 +1,156 @@
+// 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.
+
+#include "media/base/download_rate_monitor.h"
+
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using ::testing::Mock;
+
+namespace media {
+
+class DownloadRateMonitorTest : public ::testing::Test {
+ public:
+  DownloadRateMonitorTest() {
+    monitor_.set_total_bytes(kMediaSizeInBytes);
+  }
+
+  virtual ~DownloadRateMonitorTest() { }
+
+  MOCK_METHOD0(CanPlayThrough, void());
+
+ protected:
+  static const int kMediaSizeInBytes = 20 * 1024 * 1024;
+
+  // Simulates downloading of the media file. Packets are timed evenly in
+  // |ms_between_packets| intervals, starting at |starting_time|, which is
+  // number of seconds since unix epoch (Jan 1, 1970).
+  // Returns the number of bytes buffered in the media file after the
+  // network activity.
+  int SimulateNetwork(double starting_time,
+                      int starting_bytes,
+                      int bytes_per_packet,
+                      int ms_between_packets,
+                      int number_of_packets) {
+    int bytes_buffered = starting_bytes;
+    base::Time packet_time = base::Time::FromDoubleT(starting_time);
+
+    monitor_.SetNetworkActivity(true);
+    // Loop executes (number_of_packets + 1) times because a packet needs a
+    // starting and end point.
+    for (int i = 0; i < number_of_packets + 1; ++i) {
+      monitor_.SetBufferedBytes(bytes_buffered, packet_time);
+      packet_time += base::TimeDelta::FromMilliseconds(ms_between_packets);
+      bytes_buffered += bytes_per_packet;
+    }
+    monitor_.SetNetworkActivity(false);
+    return bytes_buffered;
+  }
+
+  DownloadRateMonitor monitor_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DownloadRateMonitorTest);
+};
+
+TEST_F(DownloadRateMonitorTest, DownloadRateGreaterThanBitrate) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+
+  // Simulate downloading at double the media's bitrate.
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  EXPECT_CALL(*this, CanPlayThrough());
+  SimulateNetwork(1, 0, 2 * media_bitrate / 8, 1000, 10);
+}
+
+// If the user pauses and the pipeline stops downloading data, make sure the
+// DownloadRateMonitor understands that the download is not stalling.
+TEST_F(DownloadRateMonitorTest, DownloadRateGreaterThanBitrate_Pause) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+  static const int download_byte_rate = 1.1 * media_bitrate / 8;
+
+  // Start downloading faster than the media's bitrate.
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  EXPECT_CALL(*this, CanPlayThrough());
+  int buffered = SimulateNetwork(1, 0, download_byte_rate, 1000, 2);
+
+  // Then "pause" for 3 minutes and continue downloading at same rate.
+  SimulateNetwork(60 * 3, buffered, download_byte_rate, 1000, 4);
+}
+
+TEST_F(DownloadRateMonitorTest, DownloadRateGreaterThanBitrate_SeekForward) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+  static const int download_byte_rate = 1.1 * media_bitrate / 8;
+
+  // Start downloading faster than the media's bitrate.
+  EXPECT_CALL(*this, CanPlayThrough());
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  SimulateNetwork(1, 0, download_byte_rate, 1000, 2);
+
+  // Then seek forward mid-file and continue downloading at same rate.
+  SimulateNetwork(4, kMediaSizeInBytes / 2, download_byte_rate, 1000, 4);
+}
+
+TEST_F(DownloadRateMonitorTest, DownloadRateGreaterThanBitrate_SeekBackward) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+  static const int download_byte_rate = 1.1 * media_bitrate / 8;
+
+  // Start downloading faster than the media's bitrate, in middle of file.
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  SimulateNetwork(1, kMediaSizeInBytes / 2, download_byte_rate, 1000, 2);
+
+  // Then seek back to beginning and continue downloading at same rate.
+  EXPECT_CALL(*this, CanPlayThrough());
+  SimulateNetwork(4, 0, download_byte_rate, 1000, 4);
+}
+
+TEST_F(DownloadRateMonitorTest, DownloadRateLessThanBitrate) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+
+  // Simulate downloading at half the media's bitrate.
+  EXPECT_CALL(*this, CanPlayThrough())
+      .Times(0);
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  SimulateNetwork(1, 0, media_bitrate / 8 / 2, 1000, 10);
+}
+
+TEST_F(DownloadRateMonitorTest, MediaIsLoaded) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+
+  monitor_.set_loaded(true);
+
+  // Simulate no data downloaded (source is already loaded).
+  EXPECT_CALL(*this, CanPlayThrough());
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  SimulateNetwork(1, 0, 0, 1000, 10);
+}
+
+TEST_F(DownloadRateMonitorTest, VeryFastDownloadRate) {
+  static const int media_bitrate = 1024 * 1024 * 8;
+
+  // Simulate downloading half the video very quickly in one chunk.
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  EXPECT_CALL(*this, CanPlayThrough());
+  SimulateNetwork(1, 0, kMediaSizeInBytes / 2, 10, 1);
+}
+
+TEST_F(DownloadRateMonitorTest, DownloadEntireVideo) {
+  static const int seconds_of_data = 20;
+  static const int media_bitrate = kMediaSizeInBytes * 8 / seconds_of_data;
+
+  // Simulate downloading entire video at half the bitrate of the video.
+  monitor_.Start(base::Bind(&DownloadRateMonitorTest::CanPlayThrough,
+                            base::Unretained(this)), media_bitrate);
+  EXPECT_CALL(*this, CanPlayThrough());
+  SimulateNetwork(1, 0, media_bitrate / 8 / 2, 1000, seconds_of_data * 2);
+}
+
+}  // namespace media
diff --git a/media/base/mock_filters.h b/media/base/mock_filters.h
index 841629d..f54a114 100644
--- a/media/base/mock_filters.h
+++ b/media/base/mock_filters.h
@@ -112,6 +112,7 @@ class MockDemuxer : public Demuxer {
   MOCK_METHOD1(SetPreload, void(Preload preload));
   MOCK_METHOD2(Seek, void(base::TimeDelta time, const FilterStatusCB& cb));
   MOCK_METHOD0(OnAudioRendererDisabled, void());
+  MOCK_METHOD0(GetBitrate, int());
 
   // Demuxer implementation.
   MOCK_METHOD2(Initialize, void(DataSource* data_source,
diff --git a/media/base/pipeline.h b/media/base/pipeline.h
index 7cf5e73..1c91f80 100644
--- a/media/base/pipeline.h
+++ b/media/base/pipeline.h
@@ -34,15 +34,19 @@ struct PipelineStatistics {
   uint32 video_frames_dropped;
 };
 
+enum NetworkEvent {
+  DOWNLOAD_CONTINUED,
+  DOWNLOAD_PAUSED,
+  CAN_PLAY_THROUGH
+};
+
 class FilterCollection;
 
 class MEDIA_EXPORT Pipeline : public base::RefCountedThreadSafe<Pipeline> {
  public:
   // Callback that executes when a network event occurrs.
-  // The parameter represents the state of network activity: true if the network
-  // is downloading data, false if it is not. If the callback never runs, it is
-  // assumed the network is not downloading data.
-  typedef base::Callback<void(bool)> NetworkEventCB;
+  // The parameter specifies the type of event that is being signaled.
+  typedef base::Callback<void(NetworkEvent)> NetworkEventCB;
 
   // Initializes pipeline. Pipeline takes ownership of all callbacks passed
   // into this method.
diff --git a/media/base/pipeline_impl.cc b/media/base/pipeline_impl.cc
index e0d8270..386b064 100644
--- a/media/base/pipeline_impl.cc
+++ b/media/base/pipeline_impl.cc
@@ -143,6 +143,8 @@ void PipelineImpl::Seek(base::TimeDelta time,
     return;
   }
 
+  download_rate_monitor_.Stop();
+
   message_loop_->PostTask(FROM_HERE,
       base::Bind(&PipelineImpl::SeekTask, this, time, seek_callback));
 }
@@ -186,9 +188,8 @@ float PipelineImpl::GetPlaybackRate() const {
 }
 
 void PipelineImpl::SetPlaybackRate(float playback_rate) {
-  if (playback_rate < 0.0f) {
+  if (playback_rate < 0.0f)
     return;
-  }
 
   base::AutoLock auto_lock(lock_);
   playback_rate_ = playback_rate;
@@ -204,9 +205,8 @@ float PipelineImpl::GetVolume() const {
 }
 
 void PipelineImpl::SetVolume(float volume) {
-  if (volume < 0.0f || volume > 1.0f) {
+  if (volume < 0.0f || volume > 1.0f)
     return;
-  }
 
   base::AutoLock auto_lock(lock_);
   volume_ = volume;
@@ -239,6 +239,7 @@ base::TimeDelta PipelineImpl::GetCurrentTime() const {
 }
 
 base::TimeDelta PipelineImpl::GetCurrentTime_Locked() const {
+  lock_.AssertAcquired();
   base::TimeDelta elapsed = clock_->Elapsed();
   if (state_ == kEnded || elapsed > duration_) {
     return duration_;
@@ -258,9 +259,8 @@ base::TimeDelta PipelineImpl::GetBufferedTime() {
   base::TimeDelta current_time = GetCurrentTime_Locked();
 
   // If buffered time was set, we report that value directly.
-  if (buffered_time_.ToInternalValue() > 0) {
+  if (buffered_time_.ToInternalValue() > 0)
     return std::max(buffered_time_, current_time);
-  }
 
   if (total_bytes_ == 0)
     return base::TimeDelta();
@@ -371,6 +371,7 @@ void PipelineImpl::ResetState() {
   waiting_for_clock_update_ = false;
   audio_disabled_   = false;
   clock_->SetTime(kZero);
+  download_rate_monitor_.Reset();
 }
 
 void PipelineImpl::SetState(State next_state) {
@@ -524,16 +525,17 @@ void PipelineImpl::SetTotalBytes(int64 total_bytes) {
 
   base::AutoLock auto_lock(lock_);
   total_bytes_ = total_bytes;
+  download_rate_monitor_.set_total_bytes(total_bytes_);
 }
 
 void PipelineImpl::SetBufferedBytes(int64 buffered_bytes) {
   DCHECK(IsRunning());
   base::AutoLock auto_lock(lock_);
-
   // See comments in SetCurrentReadPosition() about capping.
   if (buffered_bytes < current_bytes_)
     current_bytes_ = buffered_bytes;
   buffered_bytes_ = buffered_bytes;
+  download_rate_monitor_.SetBufferedBytes(buffered_bytes, base::Time::Now());
 }
 
 void PipelineImpl::SetNaturalVideoSize(const gfx::Size& size) {
@@ -570,13 +572,24 @@ void PipelineImpl::SetLoaded(bool loaded) {
 
   base::AutoLock auto_lock(lock_);
   loaded_ = loaded;
+  download_rate_monitor_.set_loaded(loaded_);
 }
 
 void PipelineImpl::SetNetworkActivity(bool is_downloading_data) {
   DCHECK(IsRunning());
+
+  NetworkEvent type = DOWNLOAD_PAUSED;
+  if (is_downloading_data)
+    type = DOWNLOAD_CONTINUED;
+
+  {
+    base::AutoLock auto_lock(lock_);
+    download_rate_monitor_.SetNetworkActivity(is_downloading_data);
+  }
+
   message_loop_->PostTask(FROM_HERE,
       base::Bind(
-          &PipelineImpl::NotifyNetworkEventTask, this, is_downloading_data));
+          &PipelineImpl::NotifyNetworkEventTask, this, type));
   media_log_->AddEvent(
       media_log_->CreateBooleanEvent(
           MediaLogEvent::NETWORK_ACTIVITY_SET,
@@ -682,7 +695,6 @@ void PipelineImpl::InitializeTask() {
          state_ == kInitVideoDecoder ||
          state_ == kInitVideoRenderer);
 
-
   // Demuxer created, create audio decoder.
   if (state_ == kInitDemuxer) {
     SetState(kInitAudioDecoder);
@@ -940,10 +952,10 @@ void PipelineImpl::NotifyEndedTask() {
   }
 }
 
-void PipelineImpl::NotifyNetworkEventTask(bool is_downloading_data) {
+void PipelineImpl::NotifyNetworkEventTask(NetworkEvent type) {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
   if (!network_callback_.is_null())
-    network_callback_.Run(is_downloading_data);
+    network_callback_.Run(type);
 }
 
 void PipelineImpl::DisableAudioRendererTask() {
@@ -1030,6 +1042,16 @@ void PipelineImpl::FilterStateTransitionTask() {
     if (!waiting_for_clock_update_)
       clock_->Play();
 
+    // Start monitoring rate of downloading.
+    int bitrate = 0;
+    if (demuxer_.get())
+      bitrate = demuxer_->GetBitrate();
+    // Needs to be locked because most other calls to |download_rate_monitor_|
+    // occur on the renderer thread.
+    download_rate_monitor_.Start(
+        base::Bind(&PipelineImpl::OnCanPlayThrough, this), bitrate);
+    download_rate_monitor_.SetBufferedBytes(buffered_bytes_, base::Time::Now());
+
     if (IsPipelineStopPending()) {
       // We had a pending stop request need to be honored right now.
       TearDownPipeline();
@@ -1405,4 +1427,14 @@ void PipelineImpl::OnAudioUnderflow() {
     audio_renderer_->ResumeAfterUnderflow(true);
 }
 
+void PipelineImpl::OnCanPlayThrough() {
+  message_loop_->PostTask(FROM_HERE,
+      base::Bind(&PipelineImpl::NotifyCanPlayThrough, this));
+}
+
+void PipelineImpl::NotifyCanPlayThrough() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+  NotifyNetworkEventTask(CAN_PLAY_THROUGH);
+}
+
 }  // namespace media
diff --git a/media/base/pipeline_impl.h b/media/base/pipeline_impl.h
index 084e1cd..57f8aebd 100644
--- a/media/base/pipeline_impl.h
+++ b/media/base/pipeline_impl.h
@@ -23,6 +23,7 @@
 #include "media/base/clock.h"
 #include "media/base/composite_filter.h"
 #include "media/base/demuxer.h"
+#include "media/base/download_rate_monitor.h"
 #include "media/base/filter_host.h"
 #include "media/base/pipeline.h"
 #include "ui/gfx/size.h"
@@ -261,7 +262,7 @@ class MEDIA_EXPORT PipelineImpl : public Pipeline, public FilterHost {
   void NotifyEndedTask();
 
   // Carries out handling a notification of network event.
-  void NotifyNetworkEventTask(bool is_downloading_data);
+  void NotifyNetworkEventTask(NetworkEvent type);
 
   // Carries out disabling the audio renderer.
   void DisableAudioRendererTask();
@@ -334,6 +335,14 @@ class MEDIA_EXPORT PipelineImpl : public Pipeline, public FilterHost {
 
   void OnAudioUnderflow();
 
+  // Called when |download_rate_monitor_| believes that the media can
+  // be played through without needing to pause to buffer.
+  void OnCanPlayThrough();
+
+  // Carries out the notification that the media can be played through without
+  // needing to pause to buffer.
+  void NotifyCanPlayThrough();
+
   // Message loop used to execute pipeline tasks.
   MessageLoop* message_loop_;
 
@@ -479,6 +488,12 @@ class MEDIA_EXPORT PipelineImpl : public Pipeline, public FilterHost {
   // reaches "kStarted", at which point it is used & zeroed out.
   base::Time creation_time_;
 
+  // Approximates the rate at which the media is being downloaded.
+  DownloadRateMonitor download_rate_monitor_;
+
+  // True if the pipeline is actively downloading bytes, false otherwise.
+  bool is_downloading_data_;
+
   FRIEND_TEST_ALL_PREFIXES(PipelineImplTest, GetBufferedTime);
 
   DISALLOW_COPY_AND_ASSIGN(PipelineImpl);
diff --git a/media/filters/chunk_demuxer.cc b/media/filters/chunk_demuxer.cc
index 0df22a5..c27c490 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -364,6 +364,11 @@ void ChunkDemuxer::OnAudioRendererDisabled() {
 
 void ChunkDemuxer::SetPreload(Preload preload) {}
 
+int ChunkDemuxer::GetBitrate() {
+  // TODO(acolwell): Implement bitrate reporting.
+  return 0;
+}
+
 // Demuxer implementation.
 scoped_refptr<DemuxerStream> ChunkDemuxer::GetStream(
     DemuxerStream::Type type) {
diff --git a/media/filters/chunk_demuxer.h b/media/filters/chunk_demuxer.h
index 63dd7b1..a940100 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -38,6 +38,7 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
       DemuxerStream::Type type) OVERRIDE;
   virtual void SetPreload(Preload preload) OVERRIDE;
   virtual base::TimeDelta GetStartTime() const OVERRIDE;
+  virtual int GetBitrate() OVERRIDE;
 
   // Methods used by an external object to control this demuxer.
   void FlushData();
diff --git a/media/filters/dummy_demuxer.cc b/media/filters/dummy_demuxer.cc
index 24307b9..095ffee 100644
--- a/media/filters/dummy_demuxer.cc
+++ b/media/filters/dummy_demuxer.cc
@@ -48,6 +48,10 @@ DummyDemuxer::~DummyDemuxer() {}
 
 void DummyDemuxer::SetPreload(Preload preload) {}
 
+int DummyDemuxer::GetBitrate() {
+  return 0;
+}
+
 scoped_refptr<DemuxerStream> DummyDemuxer::GetStream(DemuxerStream::Type type) {
   return streams_[type];
 }
diff --git a/media/filters/dummy_demuxer.h b/media/filters/dummy_demuxer.h
index b029aa5..309dded 100644
--- a/media/filters/dummy_demuxer.h
+++ b/media/filters/dummy_demuxer.h
@@ -48,6 +48,7 @@ class DummyDemuxer : public Demuxer {
       DemuxerStream::Type type) OVERRIDE;
   virtual void SetPreload(Preload preload) OVERRIDE;
   virtual base::TimeDelta GetStartTime() const OVERRIDE;
+  virtual int GetBitrate() OVERRIDE;
 
  private:
   bool has_video_;
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index ddfe51e..0cff00f 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -147,6 +147,7 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer, public FFmpegURLProtocol {
       DemuxerStream::Type type) OVERRIDE;
   virtual void SetPreload(Preload preload) OVERRIDE;
   virtual base::TimeDelta GetStartTime() const OVERRIDE;
+  virtual int GetBitrate() OVERRIDE;
 
   // FFmpegURLProtocol implementation.
   virtual size_t Read(size_t size, uint8* data) OVERRIDE;
@@ -161,10 +162,6 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer, public FFmpegURLProtocol {
   // For testing purposes.
   void disable_first_seek_hack_for_testing() { first_seek_hack_ = false; }
 
-  // Returns the bitrate of media file. May be obtained from container or
-  // approximated. Returns 0 if it is unknown.
-  int GetBitrate();
-
  private:
   // Only allow a factory to create this class.
   friend class MockFFmpegDemuxer;
diff --git a/media/media.gyp b/media/media.gyp
index e99dd28..b47be2c 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -116,6 +116,8 @@
         'base/demuxer_stream.h',
         'base/djb2.cc',
         'base/djb2.h',
+        'base/download_rate_monitor.cc',
+        'base/download_rate_monitor.h',
         'base/filter_collection.cc',
         'base/filter_collection.h',
         'base/filter_factories.cc',
@@ -573,6 +575,7 @@
         'base/composite_filter_unittest.cc',
         'base/data_buffer_unittest.cc',
         'base/djb2_unittest.cc',
+        'base/download_rate_monitor_unittest.cc',
         'base/filter_collection_unittest.cc',
         'base/h264_bitstream_converter_unittest.cc',
         'base/mock_reader.h',