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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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Add m-esr52 at 52.6.0
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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_