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
13 namespace webrtc {
14
VCMInterFrameDelay(int64_t currentWallClock)15 VCMInterFrameDelay::VCMInterFrameDelay(int64_t currentWallClock) {
16 Reset(currentWallClock);
17 }
18
19 // Resets the delay estimate
Reset(int64_t currentWallClock)20 void 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.
CalculateDelay(uint32_t timestamp,int64_t * delay,int64_t currentWallClock)30 bool 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
CurrentTimeStampDiffMs() const77 uint32_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.
CheckForWrapArounds(uint32_t timestamp)87 void 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