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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 rtc::TimeMicros (system monotonic | |
perkj_webrtc
2016/09/12 09:33:46
should use
nisse-webrtc
2016/09/12 12:04:20
Done.
| |
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 larger than the previous | |
50 // timestamp but no larger than |system_time_us|. | |
perkj_webrtc
2016/09/12 09:33:46
nit: Can you refrase this to say that the return v
nisse-webrtc
2016/09/12 12:04:20
It's a bit more complicated than that, but I've gi
| |
31 int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us); | 51 int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us); |
32 | 52 |
33 private: | 53 private: |
34 // State for the timestamp translation. | 54 // State for the timestamp translation. |
35 int frames_seen_; | 55 int frames_seen_; |
36 // Estimated offset between camera time and system monotonic time. | 56 // Estimated offset between camera time and system monotonic time. |
37 int64_t offset_us_; | 57 int64_t offset_us_; |
38 | 58 |
39 // State for timestamp clipping, applied after the filter, to ensure | 59 // State for the ClipTimestamp method, applied after the filter. |
40 // that translated timestamps are monotonic and not in the future. | 60 |
perkj_webrtc
2016/09/12 09:33:46
nit: remove empty line.
nisse-webrtc
2016/09/12 12:04:20
Done. I was thinking of that line as a heading for
| |
41 // Subtracted from the translated timestamps. | 61 // A large negative camera clock drift tends to push translated |
62 // timestamps into the future. |clip_bias_us_| is subtracted from the | |
63 // translated timestamps, to get them back from the future. | |
42 int64_t clip_bias_us_; | 64 int64_t clip_bias_us_; |
43 rtc::Optional<int64_t> prev_translated_time_us_; | 65 // Used to ensure that translated timestamps are monotonous. |
66 int64_t prev_translated_time_us_; | |
44 RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner); | 67 RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner); |
45 }; | 68 }; |
46 | 69 |
47 } // namespace rtc | 70 } // namespace rtc |
48 | 71 |
49 #endif // WEBRTC_BASE_TIMESTAMPALIGNER_H_ | 72 #endif // WEBRTC_BASE_TIMESTAMPALIGNER_H_ |
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