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source: webrtc/webrtc/modules/video_coding/main/source/inter_frame_delay.cc @ 0:4bda6873e34c

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Last change on this file since 0:4bda6873e34c was 0:4bda6873e34c, checked in by Michael Prittie <mprittie@…>, 6 years ago

Scrubbed password for publication.

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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
13namespace webrtc {
14
15VCMInterFrameDelay::VCMInterFrameDelay(int64_t currentWallClock)
16{
17    Reset(currentWallClock);
18}
19
20// Resets the delay estimate
21void
22VCMInterFrameDelay::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.
33bool
34VCMInterFrameDelay::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
80uint32_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.
91void
92VCMInterFrameDelay::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}
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