зеркало из https://github.com/mozilla/gecko-dev.git
80 строки
3.2 KiB
C++
80 строки
3.2 KiB
C++
/* -*- 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 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_
|