121 lines
3.7 KiB
C++
121 lines
3.7 KiB
C++
/*
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* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "inter_frame_delay.h"
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#include "tick_time.h"
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namespace webrtc {
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VCMInterFrameDelay::VCMInterFrameDelay()
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{
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Reset();
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}
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// Resets the delay estimate
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void
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VCMInterFrameDelay::Reset()
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{
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_zeroWallClock = VCMTickTime::MillisecondTimestamp();
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_wrapArounds = 0;
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_prevWallClock = 0;
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_prevTimestamp = 0;
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_dTS = 0;
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}
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// Calculates the delay of a frame with the given timestamp.
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// This method is called when the frame is complete.
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bool
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VCMInterFrameDelay::CalculateDelay(WebRtc_UWord32 timestamp,
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WebRtc_Word64 *delay,
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WebRtc_Word64 currentWallClock /* = -1 */)
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{
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if (currentWallClock <= -1)
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{
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currentWallClock = VCMTickTime::MillisecondTimestamp();
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}
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if (_prevWallClock == 0)
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{
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// First set of data, initialization, wait for next frame
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_prevWallClock = currentWallClock;
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_prevTimestamp = timestamp;
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*delay = 0;
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return true;
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}
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WebRtc_Word32 prevWrapArounds = _wrapArounds;
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CheckForWrapArounds(timestamp);
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// This will be -1 for backward wrap arounds and +1 for forward wrap arounds
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WebRtc_Word32 wrapAroundsSincePrev = _wrapArounds - prevWrapArounds;
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// Account for reordering in jitter variance estimate in the future?
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// Note that this also captures incomplete frames which are grabbed
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// for decoding after a later frame has been complete, i.e. real
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// packet losses.
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if ((wrapAroundsSincePrev == 0 && timestamp < _prevTimestamp) || wrapAroundsSincePrev < 0)
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{
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*delay = 0;
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return false;
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}
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// Compute the compensated timestamp difference and convert it to ms and
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// round it to closest integer.
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_dTS = static_cast<WebRtc_Word64>((timestamp + wrapAroundsSincePrev *
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(static_cast<WebRtc_Word64>(1)<<32) - _prevTimestamp) / 90.0 + 0.5);
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// frameDelay is the difference of dT and dTS -- i.e. the difference of
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// the wall clock time difference and the timestamp difference between
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// two following frames.
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*delay = static_cast<WebRtc_Word64>(currentWallClock - _prevWallClock - _dTS);
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_prevTimestamp = timestamp;
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_prevWallClock = currentWallClock;
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return true;
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}
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// Returns the current difference between incoming timestamps
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WebRtc_UWord32 VCMInterFrameDelay::CurrentTimeStampDiffMs() const
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{
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if (_dTS < 0)
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{
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return 0;
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}
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return static_cast<WebRtc_UWord32>(_dTS);
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}
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// Investigates if the timestamp clock has overflowed since the last timestamp and
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// keeps track of the number of wrap arounds since reset.
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void
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VCMInterFrameDelay::CheckForWrapArounds(WebRtc_UWord32 timestamp)
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{
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if (timestamp < _prevTimestamp)
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{
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// This difference will probably be less than -2^31 if we have had a wrap around
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// (e.g. timestamp = 1, _previousTimestamp = 2^32 - 1). Since it is cast to a Word32,
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// it should be positive.
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if (static_cast<WebRtc_Word32>(timestamp - _prevTimestamp) > 0)
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{
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// Forward wrap around
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_wrapArounds++;
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}
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}
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// This difference will probably be less than -2^31 if we have had a backward wrap around.
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// Since it is cast to a Word32, it should be positive.
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else if (static_cast<WebRtc_Word32>(_prevTimestamp - timestamp) > 0)
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{
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// Backward wrap around
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_wrapArounds--;
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}
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}
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}
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