1 /* 2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "webrtc/modules/video_coding/main/source/inter_frame_delay.h" 12 13 namespace webrtc { 14 15 VCMInterFrameDelay::VCMInterFrameDelay(int64_t currentWallClock) 16 { 17 Reset(currentWallClock); 18 } 19 20 // Resets the delay estimate 21 void 22 VCMInterFrameDelay::Reset(int64_t currentWallClock) 23 { 24 _zeroWallClock = currentWallClock; 25 _wrapArounds = 0; 26 _prevWallClock = 0; 27 _prevTimestamp = 0; 28 _dTS = 0; 29 } 30 31 // Calculates the delay of a frame with the given timestamp. 32 // This method is called when the frame is complete. 33 bool 34 VCMInterFrameDelay::CalculateDelay(uint32_t timestamp, 35 int64_t *delay, 36 int64_t currentWallClock) 37 { 38 if (_prevWallClock == 0) 39 { 40 // First set of data, initialization, wait for next frame 41 _prevWallClock = currentWallClock; 42 _prevTimestamp = timestamp; 43 *delay = 0; 44 return true; 45 } 46 47 int32_t prevWrapArounds = _wrapArounds; 48 CheckForWrapArounds(timestamp); 49 50 // This will be -1 for backward wrap arounds and +1 for forward wrap arounds 51 int32_t wrapAroundsSincePrev = _wrapArounds - prevWrapArounds; 52 53 // Account for reordering in jitter variance estimate in the future? 54 // Note that this also captures incomplete frames which are grabbed 55 // for decoding after a later frame has been complete, i.e. real 56 // packet losses. 57 if ((wrapAroundsSincePrev == 0 && timestamp < _prevTimestamp) || wrapAroundsSincePrev < 0) 58 { 59 *delay = 0; 60 return false; 61 } 62 63 // Compute the compensated timestamp difference and convert it to ms and 64 // round it to closest integer. 65 _dTS = static_cast<int64_t>((timestamp + wrapAroundsSincePrev * 66 (static_cast<int64_t>(1)<<32) - _prevTimestamp) / 90.0 + 0.5); 67 68 // frameDelay is the difference of dT and dTS -- i.e. the difference of 69 // the wall clock time difference and the timestamp difference between 70 // two following frames. 71 *delay = static_cast<int64_t>(currentWallClock - _prevWallClock - _dTS); 72 73 _prevTimestamp = timestamp; 74 _prevWallClock = currentWallClock; 75 76 return true; 77 } 78 79 // Returns the current difference between incoming timestamps 80 uint32_t VCMInterFrameDelay::CurrentTimeStampDiffMs() const 81 { 82 if (_dTS < 0) 83 { 84 return 0; 85 } 86 return static_cast<uint32_t>(_dTS); 87 } 88 89 // Investigates if the timestamp clock has overflowed since the last timestamp and 90 // keeps track of the number of wrap arounds since reset. 91 void 92 VCMInterFrameDelay::CheckForWrapArounds(uint32_t timestamp) 93 { 94 if (timestamp < _prevTimestamp) 95 { 96 // This difference will probably be less than -2^31 if we have had a wrap around 97 // (e.g. timestamp = 1, _previousTimestamp = 2^32 - 1). Since it is cast to a Word32, 98 // it should be positive. 99 if (static_cast<int32_t>(timestamp - _prevTimestamp) > 0) 100 { 101 // Forward wrap around 102 _wrapArounds++; 103 } 104 } 105 // This difference will probably be less than -2^31 if we have had a backward wrap around. 106 // Since it is cast to a Word32, it should be positive. 107 else if (static_cast<int32_t>(_prevTimestamp - timestamp) > 0) 108 { 109 // Backward wrap around 110 _wrapArounds--; 111 } 112 } 113 114 } 115