OLD | NEW |
1 /* | 1 /* |
2 * Copyright (c) 2016 The WebRTC Project Authors. All rights reserved. | 2 * Copyright (c) 2016 The WebRTC Project Authors. All rights reserved. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license | 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 | 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 | 6 * tree. An additional intellectual property rights grant can be found |
7 * in the file PATENTS. All contributing project authors may | 7 * in the file PATENTS. All contributing project authors may |
8 * be found in the AUTHORS file in the root of the source tree. | 8 * be found in the AUTHORS file in the root of the source tree. |
9 */ | 9 */ |
10 | 10 |
11 #ifndef WEBRTC_BASE_TIMESTAMPALIGNER_H_ | 11 #ifndef WEBRTC_BASE_TIMESTAMPALIGNER_H_ |
12 #define WEBRTC_BASE_TIMESTAMPALIGNER_H_ | 12 #define WEBRTC_BASE_TIMESTAMPALIGNER_H_ |
13 | 13 |
14 #include "webrtc/base/basictypes.h" | 14 #include "webrtc/base/basictypes.h" |
15 #include "webrtc/base/constructormagic.h" | 15 #include "webrtc/base/constructormagic.h" |
16 #include "webrtc/base/optional.h" | |
17 | 16 |
18 namespace rtc { | 17 namespace rtc { |
19 | 18 |
| 19 // The TimestampAligner class helps translating camera timestamps into |
| 20 // the same timescale as is used by rtc::TimeMicros(). Some cameras |
| 21 // have built in timestamping which is more accurate than reading the |
| 22 // system clock, but using a different epoch and unknown clock drift. |
| 23 // Frame timestamps in webrtc should use rtc::TimeMicros (system monotonic |
| 24 // time), and this class provides a filter which lets us use the |
| 25 // rtc::TimeMicros timescale, and at the same time take advantage of |
| 26 // higher accuracy of the camera clock. |
| 27 |
20 // This class is not thread safe, so all calls to it must be synchronized | 28 // This class is not thread safe, so all calls to it must be synchronized |
21 // externally. | 29 // externally. |
22 class TimestampAligner { | 30 class TimestampAligner { |
23 public: | 31 public: |
24 TimestampAligner(); | 32 TimestampAligner(); |
25 ~TimestampAligner(); | 33 ~TimestampAligner(); |
26 | 34 |
27 public: | 35 public: |
| 36 // Translates camera timestamps to the same timescale as is used by |
| 37 // rtc::TimeMicros(). |camera_time_us| is assumed to be accurate, but |
| 38 // with an unknown epoch and clock drift. |system_time_us| is |
| 39 // time according to rtc::TimeMicros(), preferably read as soon as |
| 40 // possible when the frame is captured. It may have poor accuracy |
| 41 // due to poor resolution or scheduling delays. Returns the |
| 42 // translated timestamp. |
| 43 int64_t TranslateTimestamp(int64_t camera_time_us, int64_t system_time_us); |
| 44 |
| 45 protected: |
28 // Update the estimated offset between camera time and system monotonic time. | 46 // Update the estimated offset between camera time and system monotonic time. |
29 int64_t UpdateOffset(int64_t camera_time_us, int64_t system_time_us); | 47 int64_t UpdateOffset(int64_t camera_time_us, int64_t system_time_us); |
30 | 48 |
| 49 // Clip timestamp, return value is always |
| 50 // <= |system_time_us|, and |
| 51 // >= min(|prev_translated_time_us_| + |kMinFrameIntervalUs|, |
| 52 // |system_time_us|). |
31 int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us); | 53 int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us); |
32 | 54 |
33 private: | 55 private: |
34 // State for the timestamp translation. | 56 // State for the timestamp translation. |
35 int frames_seen_; | 57 int frames_seen_; |
36 // Estimated offset between camera time and system monotonic time. | 58 // Estimated offset between camera time and system monotonic time. |
37 int64_t offset_us_; | 59 int64_t offset_us_; |
38 | 60 |
39 // State for timestamp clipping, applied after the filter, to ensure | 61 // State for the ClipTimestamp method, applied after the filter. |
40 // that translated timestamps are monotonic and not in the future. | 62 // A large negative camera clock drift tends to push translated |
41 // Subtracted from the translated timestamps. | 63 // timestamps into the future. |clip_bias_us_| is subtracted from the |
| 64 // translated timestamps, to get them back from the future. |
42 int64_t clip_bias_us_; | 65 int64_t clip_bias_us_; |
43 rtc::Optional<int64_t> prev_translated_time_us_; | 66 // Used to ensure that translated timestamps are monotonous. |
| 67 int64_t prev_translated_time_us_; |
44 RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner); | 68 RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner); |
45 }; | 69 }; |
46 | 70 |
47 } // namespace rtc | 71 } // namespace rtc |
48 | 72 |
49 #endif // WEBRTC_BASE_TIMESTAMPALIGNER_H_ | 73 #endif // WEBRTC_BASE_TIMESTAMPALIGNER_H_ |
OLD | NEW |