1 /* 2 * Copyright (c) 2019 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 #ifndef MODULES_RTP_RTCP_SOURCE_ABSOLUTE_CAPTURE_TIME_RECEIVER_H_ 12 #define MODULES_RTP_RTCP_SOURCE_ABSOLUTE_CAPTURE_TIME_RECEIVER_H_ 13 14 #include "api/array_view.h" 15 #include "api/rtp_headers.h" 16 #include "api/units/time_delta.h" 17 #include "api/units/timestamp.h" 18 #include "rtc_base/synchronization/mutex.h" 19 #include "rtc_base/thread_annotations.h" 20 #include "system_wrappers/include/clock.h" 21 22 namespace webrtc { 23 24 // 25 // Helper class for receiving the |AbsoluteCaptureTime| header extension. 26 // 27 // Supports the "timestamp interpolation" optimization: 28 // A receiver SHOULD memorize the capture system (i.e. CSRC/SSRC), capture 29 // timestamp, and RTP timestamp of the most recently received abs-capture-time 30 // packet on each received stream. It can then use that information, in 31 // combination with RTP timestamps of packets without abs-capture-time, to 32 // extrapolate missing capture timestamps. 33 // 34 // See: https://webrtc.org/experiments/rtp-hdrext/abs-capture-time/ 35 // 36 class AbsoluteCaptureTimeReceiver { 37 public: 38 static constexpr TimeDelta kInterpolationMaxInterval = 39 TimeDelta::Millis(5000); 40 41 explicit AbsoluteCaptureTimeReceiver(Clock* clock); 42 43 // Returns the source (i.e. SSRC or CSRC) of the capture system. 44 static uint32_t GetSource(uint32_t ssrc, 45 rtc::ArrayView<const uint32_t> csrcs); 46 47 // Sets the NTP clock offset between the sender system (which may be different 48 // from the capture system) and the local system. This information is normally 49 // provided by passing half the value of the Round-Trip Time estimation given 50 // by RTCP sender reports (see DLSR/DLRR). 51 // 52 // Note that the value must be in Q32.32-formatted fixed-point seconds. 53 void SetRemoteToLocalClockOffset(absl::optional<int64_t> value_q32x32); 54 55 // Returns a received header extension, an interpolated header extension, or 56 // |absl::nullopt| if it's not possible to interpolate a header extension. 57 absl::optional<AbsoluteCaptureTime> OnReceivePacket( 58 uint32_t source, 59 uint32_t rtp_timestamp, 60 uint32_t rtp_clock_frequency, 61 const absl::optional<AbsoluteCaptureTime>& received_extension); 62 63 private: 64 friend class AbsoluteCaptureTimeSender; 65 66 static uint64_t InterpolateAbsoluteCaptureTimestamp( 67 uint32_t rtp_timestamp, 68 uint32_t rtp_clock_frequency, 69 uint32_t last_rtp_timestamp, 70 uint64_t last_absolute_capture_timestamp); 71 72 bool ShouldInterpolateExtension(Timestamp receive_time, 73 uint32_t source, 74 uint32_t rtp_timestamp, 75 uint32_t rtp_clock_frequency) const 76 RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_); 77 78 absl::optional<int64_t> AdjustEstimatedCaptureClockOffset( 79 absl::optional<int64_t> received_value) const 80 RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_); 81 82 Clock* const clock_; 83 84 Mutex mutex_; 85 86 absl::optional<int64_t> remote_to_local_clock_offset_ RTC_GUARDED_BY(mutex_); 87 88 Timestamp last_receive_time_ RTC_GUARDED_BY(mutex_); 89 90 uint32_t last_source_ RTC_GUARDED_BY(mutex_); 91 uint32_t last_rtp_timestamp_ RTC_GUARDED_BY(mutex_); 92 uint32_t last_rtp_clock_frequency_ RTC_GUARDED_BY(mutex_); 93 uint64_t last_absolute_capture_timestamp_ RTC_GUARDED_BY(mutex_); 94 absl::optional<int64_t> last_estimated_capture_clock_offset_ 95 RTC_GUARDED_BY(mutex_); 96 }; // AbsoluteCaptureTimeReceiver 97 98 } // namespace webrtc 99 100 #endif // MODULES_RTP_RTCP_SOURCE_ABSOLUTE_CAPTURE_TIME_RECEIVER_H_ 101