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