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| 1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #include "media/base/download_rate_monitor.h" |
| 6 |
| 7 #include "base/bind.h" |
| 8 #include "base/time.h" |
| 9 |
| 10 namespace media { |
| 11 |
| 12 // Number of samples to use to collect and average for each measurement of |
| 13 // download rate. |
| 14 static const size_t kNumberOfSamples = 5; |
| 15 |
| 16 // Minimum number of seconds represented in a sample period. |
| 17 static const float kSamplePeriod = 1.0; |
| 18 |
| 19 DownloadRateMonitor::Sample::Sample() { |
| 20 Reset(); |
| 21 } |
| 22 |
| 23 DownloadRateMonitor::Sample::Sample( |
| 24 const BufferingPoint& start, const BufferingPoint& end) { |
| 25 Reset(); |
| 26 start_ = start; |
| 27 set_end(end); |
| 28 } |
| 29 |
| 30 void DownloadRateMonitor::Sample::set_end(const BufferingPoint& new_end) { |
| 31 DCHECK(!start_.timestamp.is_null()); |
| 32 DCHECK(new_end.buffered_bytes >= start_.buffered_bytes); |
| 33 DCHECK(new_end.timestamp >= start_.timestamp); |
| 34 end_ = new_end; |
| 35 } |
| 36 |
| 37 float DownloadRateMonitor::Sample::bytes_per_second() const { |
| 38 if (seconds_elapsed() > 0.0 && bytes_downloaded() >= 0) |
| 39 return bytes_downloaded() / seconds_elapsed(); |
| 40 return -1.0; |
| 41 } |
| 42 |
| 43 float DownloadRateMonitor::Sample::seconds_elapsed() const { |
| 44 if (start_.timestamp.is_null() || end_.timestamp.is_null()) |
| 45 return -1.0; |
| 46 return (end_.timestamp - start_.timestamp).InSecondsF(); |
| 47 } |
| 48 |
| 49 int64 DownloadRateMonitor::Sample::bytes_downloaded() const { |
| 50 if (start_.timestamp.is_null() || end_.timestamp.is_null()) |
| 51 return -1.0; |
| 52 return end_.buffered_bytes - start_.buffered_bytes; |
| 53 } |
| 54 |
| 55 bool DownloadRateMonitor::Sample::is_null() const { |
| 56 return start_.timestamp.is_null() && end_.timestamp.is_null(); |
| 57 } |
| 58 |
| 59 void DownloadRateMonitor::Sample::Reset() { |
| 60 start_ = BufferingPoint(); |
| 61 end_ = BufferingPoint(); |
| 62 } |
| 63 |
| 64 void DownloadRateMonitor::Sample::RestartAtEndBufferingPoint() { |
| 65 start_ = end_; |
| 66 end_ = BufferingPoint(); |
| 67 } |
| 68 |
| 69 DownloadRateMonitor::DownloadRateMonitor() { |
| 70 Reset(); |
| 71 } |
| 72 |
| 73 void DownloadRateMonitor::Start( |
| 74 const base::Closure& canplaythrough_cb, int media_bitrate) { |
| 75 DCHECK(stopped_); |
| 76 canplaythrough_cb_ = canplaythrough_cb; |
| 77 stopped_ = false; |
| 78 bitrate_ = media_bitrate; |
| 79 current_sample_.Reset(); |
| 80 buffered_bytes_ = 0; |
| 81 |
| 82 NotifyCanPlayThroughIfNeeded(); |
| 83 } |
| 84 |
| 85 void DownloadRateMonitor::SetBufferedBytes( |
| 86 int64 buffered_bytes, const base::Time& timestamp) { |
| 87 if (stopped_) |
| 88 return; |
| 89 |
| 90 is_downloading_data_ = true; |
| 91 |
| 92 // Check monotonically nondecreasing constraint. |
| 93 base::Time previous_time; |
| 94 if (!current_sample_.is_null()) |
| 95 previous_time = current_sample_.end().timestamp; |
| 96 else if (!sample_window_.empty()) |
| 97 previous_time = sample_window_.back().end().timestamp; |
| 98 |
| 99 // If we go backward in time, dismiss the sample. |
| 100 if (!previous_time.is_null() && timestamp < previous_time) |
| 101 return; |
| 102 |
| 103 // If the buffer level has dropped, invalidate current sample. |
| 104 if (buffered_bytes < buffered_bytes_) |
| 105 current_sample_.Reset(); |
| 106 buffered_bytes_ = buffered_bytes; |
| 107 |
| 108 BufferingPoint latest_point = { buffered_bytes, timestamp }; |
| 109 if (current_sample_.is_null()) |
| 110 current_sample_ = Sample(latest_point, latest_point); |
| 111 else |
| 112 current_sample_.set_end(latest_point); |
| 113 |
| 114 UpdateSampleWindow(); |
| 115 NotifyCanPlayThroughIfNeeded(); |
| 116 } |
| 117 |
| 118 void DownloadRateMonitor::SetNetworkActivity(bool is_downloading_data) { |
| 119 if (is_downloading_data == is_downloading_data_) |
| 120 return; |
| 121 // Invalidate the current sample if downloading is going from start to stopped |
| 122 // or vice versa. |
| 123 current_sample_.Reset(); |
| 124 is_downloading_data_ = is_downloading_data; |
| 125 } |
| 126 |
| 127 void DownloadRateMonitor::Stop() { |
| 128 stopped_ = true; |
| 129 current_sample_.Reset(); |
| 130 buffered_bytes_ = 0; |
| 131 } |
| 132 |
| 133 void DownloadRateMonitor::Reset() { |
| 134 canplaythrough_cb_.Reset(); |
| 135 has_notified_can_play_through_ = false; |
| 136 current_sample_.Reset(); |
| 137 sample_window_.clear(); |
| 138 is_downloading_data_ = false; |
| 139 total_bytes_ = 0; |
| 140 buffered_bytes_ = 0; |
| 141 loaded_ = false; |
| 142 bitrate_ = 0; |
| 143 stopped_ = true; |
| 144 } |
| 145 |
| 146 int64 DownloadRateMonitor::bytes_downloaded_in_window() const { |
| 147 // There are max |kNumberOfSamples| so we might as well recompute each time. |
| 148 int64 total = 0; |
| 149 for (size_t i = 0; i < sample_window_.size(); ++i) |
| 150 total += sample_window_[i].bytes_downloaded(); |
| 151 return total; |
| 152 } |
| 153 |
| 154 float DownloadRateMonitor::seconds_elapsed_in_window() const { |
| 155 // There are max |kNumberOfSamples| so we might as well recompute each time. |
| 156 float total = 0.0; |
| 157 for (size_t i = 0; i < sample_window_.size(); ++i) |
| 158 total += sample_window_[i].seconds_elapsed(); |
| 159 return total; |
| 160 } |
| 161 |
| 162 void DownloadRateMonitor::UpdateSampleWindow() { |
| 163 if (current_sample_.seconds_elapsed() < kSamplePeriod) |
| 164 return; |
| 165 |
| 166 // Add latest sample and remove oldest sample. |
| 167 sample_window_.push_back(current_sample_); |
| 168 if (sample_window_.size() > kNumberOfSamples) |
| 169 sample_window_.pop_front(); |
| 170 |
| 171 // Prepare for next measurement. |
| 172 current_sample_.RestartAtEndBufferingPoint(); |
| 173 } |
| 174 |
| 175 float DownloadRateMonitor::ApproximateDownloadByteRate() const { |
| 176 // Compute and return the average download byte rate from within the sample |
| 177 // window. |
| 178 // NOTE: In the unlikely case where the data is arriving really bursty-ly, |
| 179 // say getting a big chunk of data every 5 seconds, then with this |
| 180 // implementation it will take 25 seconds until bitrate is calculated. |
| 181 if (sample_window_.size() >= kNumberOfSamples && |
| 182 seconds_elapsed_in_window() > 0.0) { |
| 183 return bytes_downloaded_in_window() / seconds_elapsed_in_window(); |
| 184 } |
| 185 |
| 186 // Could not determine approximate download byte rate. |
| 187 return -1.0; |
| 188 } |
| 189 |
| 190 bool DownloadRateMonitor::ShouldNotifyCanPlayThrough() { |
| 191 // A stream with |total_bytes_| == 0 means the size of the stream cannot be |
| 192 // determined or is undefined in the streaming case. In these scenarios, |
| 193 // CanPlayThrough should never fire. |
| 194 if (has_notified_can_play_through_ || total_bytes_ == 0) |
| 195 return false; |
| 196 |
| 197 // If the media is from a local file (|loaded_|) or if all bytes are |
| 198 // buffered, fire CanPlayThrough. |
| 199 if (loaded_ || buffered_bytes_ == total_bytes_) |
| 200 return true; |
| 201 |
| 202 // Cannot approximate when the media can play through if bitrate is unknown. |
| 203 if (bitrate_ <= 0) |
| 204 return false; |
| 205 |
| 206 float bytes_needed_per_second = bitrate_ / 8; |
| 207 float download_rate = ApproximateDownloadByteRate(); |
| 208 |
| 209 // If we are downloading at or faster than the media's bitrate, then we can |
| 210 // play through to the end of the media without stopping to buffer. |
| 211 if (download_rate > 0) |
| 212 return download_rate >= bytes_needed_per_second; |
| 213 |
| 214 // If download rate is unknown, it may be because the media is being |
| 215 // downloaded so fast that it cannot collect an adequate number of samples |
| 216 // before the download gets deferred. |
| 217 // |
| 218 // To catch this case, we also look at how much data is being downloaded |
| 219 // immediately after the download begins. |
| 220 if (sample_window_.size() < kNumberOfSamples) { |
| 221 int64 bytes_downloaded_since_start = |
| 222 bytes_downloaded_in_window() + current_sample_.bytes_downloaded(); |
| 223 float seconds_elapsed_since_start = |
| 224 seconds_elapsed_in_window() + current_sample_.seconds_elapsed(); |
| 225 |
| 226 // If we download 4 seconds of data in less than 2 seconds of time, we're |
| 227 // probably downloading at a fast enough rate that we can play through. |
| 228 // This is an arbitrary metric that will likely need tweaking. |
| 229 if (seconds_elapsed_since_start < 2.0 && |
| 230 bytes_downloaded_since_start > 4.0 * bytes_needed_per_second) { |
| 231 return true; |
| 232 } |
| 233 } |
| 234 |
| 235 return false; |
| 236 } |
| 237 |
| 238 void DownloadRateMonitor::NotifyCanPlayThroughIfNeeded() { |
| 239 if (ShouldNotifyCanPlayThrough() && !canplaythrough_cb_.is_null()) { |
| 240 canplaythrough_cb_.Run(); |
| 241 has_notified_can_play_through_ = true; |
| 242 } |
| 243 } |
| 244 |
| 245 } // namespace media |
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