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