95 lines
3.3 KiB
C++
95 lines
3.3 KiB
C++
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/*
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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 "modules/video_coding/inter_frame_delay.h"
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namespace webrtc {
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VCMInterFrameDelay::VCMInterFrameDelay(int64_t currentWallClock) {
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Reset(currentWallClock);
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}
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// Resets the delay estimate.
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void VCMInterFrameDelay::Reset(int64_t currentWallClock) {
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_zeroWallClock = currentWallClock;
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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 VCMInterFrameDelay::CalculateDelay(uint32_t timestamp,
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int64_t* delay,
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int64_t currentWallClock) {
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if (_prevWallClock == 0) {
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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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int32_t 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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int32_t 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 for
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// decoding after a later frame has been complete, i.e. real packet losses.
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if ((wrapAroundsSincePrev == 0 && timestamp < _prevTimestamp) ||
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wrapAroundsSincePrev < 0) {
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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 round
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// it to closest integer.
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_dTS = static_cast<int64_t>(
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(timestamp + wrapAroundsSincePrev * (static_cast<int64_t>(1) << 32) -
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_prevTimestamp) /
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90.0 +
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0.5);
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// frameDelay is the difference of dT and dTS -- i.e. the difference of the
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// wall clock time difference and the timestamp difference between two
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// following frames.
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*delay = static_cast<int64_t>(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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// Investigates if the timestamp clock has overflowed since the last timestamp
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// and keeps track of the number of wrap arounds since reset.
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void VCMInterFrameDelay::CheckForWrapArounds(uint32_t timestamp) {
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if (timestamp < _prevTimestamp) {
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// This difference will probably be less than -2^31 if we have had a wrap
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// around (e.g. timestamp = 1, _prevTimestamp = 2^32 - 1). Since it is cast
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// to a int32_t, it should be positive.
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if (static_cast<int32_t>(timestamp - _prevTimestamp) > 0) {
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// Forward wrap around.
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_wrapArounds++;
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}
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// This difference will probably be less than -2^31 if we have had a
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// backward wrap around. Since it is cast to a int32_t, it should be
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// positive.
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} else if (static_cast<int32_t>(_prevTimestamp - timestamp) > 0) {
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// Backward wrap around.
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_wrapArounds--;
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}
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}
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} // namespace webrtc
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