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 "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 for
49 // decoding after a later frame has been complete, i.e. real packet losses.
50 if ((wrapAroundsSincePrev == 0 && timestamp < _prevTimestamp) ||
51 wrapAroundsSincePrev < 0) {
52 *delay = 0;
53 return false;
54 }
55
56 // Compute the compensated timestamp difference and convert it to ms and round
57 // it to closest integer.
58 _dTS = static_cast<int64_t>(
59 (timestamp + wrapAroundsSincePrev * (static_cast<int64_t>(1) << 32) -
60 _prevTimestamp) /
61 90.0 +
62 0.5);
63
64 // frameDelay is the difference of dT and dTS -- i.e. the difference of the
65 // wall clock time difference and the timestamp difference between two
66 // following frames.
67 *delay = static_cast<int64_t>(currentWallClock - _prevWallClock - _dTS);
68
69 _prevTimestamp = timestamp;
70 _prevWallClock = currentWallClock;
71
72 return true;
73 }
74
75 // Investigates if the timestamp clock has overflowed since the last timestamp
76 // and keeps track of the number of wrap arounds since reset.
CheckForWrapArounds(uint32_t timestamp)77 void VCMInterFrameDelay::CheckForWrapArounds(uint32_t timestamp) {
78 if (timestamp < _prevTimestamp) {
79 // This difference will probably be less than -2^31 if we have had a wrap
80 // around (e.g. timestamp = 1, _prevTimestamp = 2^32 - 1). Since it is cast
81 // to a int32_t, it should be positive.
82 if (static_cast<int32_t>(timestamp - _prevTimestamp) > 0) {
83 // Forward wrap around.
84 _wrapArounds++;
85 }
86 // This difference will probably be less than -2^31 if we have had a
87 // backward wrap around. Since it is cast to a int32_t, it should be
88 // positive.
89 } else if (static_cast<int32_t>(_prevTimestamp - timestamp) > 0) {
90 // Backward wrap around.
91 _wrapArounds--;
92 }
93 }
94 } // namespace webrtc
95