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diff --git a/dom/media/MediaStatistics.h b/dom/media/MediaStatistics.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MediaStatistics_h_
+#define MediaStatistics_h_
+
+namespace mozilla {
+
+struct MediaStatistics {
+  // Estimate of the current playback rate (bytes/second).
+  double mPlaybackRate;
+  // Estimate of the current download rate (bytes/second). This
+  // ignores time that the channel was paused by Gecko.
+  double mDownloadRate;
+  // Total length of media stream in bytes; -1 if not known
+  int64_t mTotalBytes;
+  // Current position of the download, in bytes. This is the offset of
+  // the first uncached byte after the decoder position.
+  int64_t mDownloadPosition;
+  // Current position of decoding, in bytes (how much of the stream
+  // has been consumed)
+  int64_t mDecoderPosition;
+  // Current position of playback, in bytes
+  int64_t mPlaybackPosition;
+  // If false, then mDownloadRate cannot be considered a reliable
+  // estimate (probably because the download has only been running
+  // a short time).
+  bool mDownloadRateReliable;
+  // If false, then mPlaybackRate cannot be considered a reliable
+  // estimate (probably because playback has only been running
+  // a short time).
+  bool mPlaybackRateReliable;
+
+  bool CanPlayThrough()
+  {
+    // Number of estimated seconds worth of data we need to have buffered
+    // ahead of the current playback position before we allow the media decoder
+    // to report that it can play through the entire media without the decode
+    // catching up with the download. Having this margin make the
+    // CanPlayThrough() calculation more stable in the case of
+    // fluctuating bitrates.
+    static const int64_t CAN_PLAY_THROUGH_MARGIN = 1;
+
+    if ((mTotalBytes < 0 && mDownloadRateReliable) ||
+        (mTotalBytes >= 0 && mTotalBytes == mDownloadPosition)) {
+      return true;
+    }
+
+    if (!mDownloadRateReliable || !mPlaybackRateReliable) {
+      return false;
+    }
+
+    int64_t bytesToDownload = mTotalBytes - mDownloadPosition;
+    int64_t bytesToPlayback = mTotalBytes - mPlaybackPosition;
+    double timeToDownload = bytesToDownload / mDownloadRate;
+    double timeToPlay = bytesToPlayback / mPlaybackRate;
+
+    if (timeToDownload > timeToPlay) {
+      // Estimated time to download is greater than the estimated time to play.
+      // We probably can't play through without having to stop to buffer.
+      return false;
+    }
+
+    // Estimated time to download is less than the estimated time to play.
+    // We can probably play through without having to buffer, but ensure that
+    // we've got a reasonable amount of data buffered after the current
+    // playback position, so that if the bitrate of the media fluctuates, or if
+    // our download rate or decode rate estimation is otherwise inaccurate,
+    // we don't suddenly discover that we need to buffer. This is particularly
+    // required near the start of the media, when not much data is downloaded.
+    int64_t readAheadMargin =
+      static_cast<int64_t>(mPlaybackRate * CAN_PLAY_THROUGH_MARGIN);
+    return mDownloadPosition > mPlaybackPosition + readAheadMargin;
+  }
+};
+
+} // namespace mozilla
+
+#endif // MediaStatistics_h_