Add clock skew estimate between sender and receiver in RemoteNtpTimeEstimator.
Bug: webrtc:11342
Change-Id: Ied155984794670ad08a663ac71f98719e96f8037
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168223
Commit-Queue: Minyue Li <minyue@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Chen Xing <chxg@google.com>
Cr-Commit-Position: refs/heads/master@{#30474}
diff --git a/modules/rtp_rtcp/include/remote_ntp_time_estimator.h b/modules/rtp_rtcp/include/remote_ntp_time_estimator.h
index dd0e0de..6112e54 100644
--- a/modules/rtp_rtcp/include/remote_ntp_time_estimator.h
+++ b/modules/rtp_rtcp/include/remote_ntp_time_estimator.h
@@ -13,6 +13,7 @@
#include <stdint.h>
+#include "absl/types/optional.h"
#include "rtc_base/constructor_magic.h"
#include "rtc_base/numerics/moving_median_filter.h"
#include "system_wrappers/include/rtp_to_ntp_estimator.h"
@@ -32,7 +33,7 @@
~RemoteNtpTimeEstimator();
// Updates the estimator with round trip time |rtt|, NTP seconds |ntp_secs|,
- // NTP fraction |ntp_frac| and RTP timestamp |rtcp_timestamp|.
+ // NTP fraction |ntp_frac| and RTP timestamp |rtp_timestamp|.
bool UpdateRtcpTimestamp(int64_t rtt,
uint32_t ntp_secs,
uint32_t ntp_frac,
@@ -42,6 +43,10 @@
// Returns the NTP timestamp in ms when success. -1 if failed.
int64_t Estimate(uint32_t rtp_timestamp);
+ // Estimates the offset, in milliseconds, between the remote clock and the
+ // local one. This is equal to local NTP clock - remote NTP clock.
+ absl::optional<int64_t> EstimateRemoteToLocalClockOffsetMs();
+
private:
Clock* clock_;
MovingMedianFilter<int64_t> ntp_clocks_offset_estimator_;
diff --git a/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc b/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc
index fd19b13..6fed731 100644
--- a/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc
+++ b/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc
@@ -12,14 +12,17 @@
#include <cstdint>
+#include "modules/rtp_rtcp/source/time_util.h"
#include "rtc_base/logging.h"
#include "system_wrappers/include/clock.h"
namespace webrtc {
namespace {
-static const int kTimingLogIntervalMs = 10000;
-static const int kClocksOffsetSmoothingWindow = 100;
+
+constexpr int kMinimumNumberOfSamples = 2;
+constexpr int kTimingLogIntervalMs = 10000;
+constexpr int kClocksOffsetSmoothingWindow = 100;
} // namespace
@@ -35,9 +38,9 @@
bool RemoteNtpTimeEstimator::UpdateRtcpTimestamp(int64_t rtt,
uint32_t ntp_secs,
uint32_t ntp_frac,
- uint32_t rtcp_timestamp) {
+ uint32_t rtp_timestamp) {
bool new_rtcp_sr = false;
- if (!rtp_to_ntp_.UpdateMeasurements(ntp_secs, ntp_frac, rtcp_timestamp,
+ if (!rtp_to_ntp_.UpdateMeasurements(ntp_secs, ntp_frac, rtp_timestamp,
&new_rtcp_sr)) {
return false;
}
@@ -47,8 +50,9 @@
}
// Update extrapolator with the new arrival time.
- // The extrapolator assumes the TimeInMilliseconds time.
- int64_t receiver_arrival_time_ms = clock_->TimeInMilliseconds();
+ // The extrapolator assumes the ntp time.
+ int64_t receiver_arrival_time_ms =
+ clock_->TimeInMilliseconds() + NtpOffsetMs();
int64_t sender_send_time_ms = Clock::NtpToMs(ntp_secs, ntp_frac);
int64_t sender_arrival_time_ms = sender_send_time_ms + rtt / 2;
int64_t remote_to_local_clocks_offset =
@@ -65,21 +69,36 @@
int64_t remote_to_local_clocks_offset =
ntp_clocks_offset_estimator_.GetFilteredValue();
- int64_t receiver_capture_ms =
+ int64_t receiver_capture_ntp_ms =
sender_capture_ntp_ms + remote_to_local_clocks_offset;
+
+ // TODO(bugs.webrtc.org/11327): Clock::CurrentNtpInMilliseconds() was
+ // previously used to calculate the offset between the local and the remote
+ // clock. However, rtc::TimeMillis() + NtpOffsetMs() is now used as the local
+ // ntp clock value. To preserve the old behavior of this method, the return
+ // value is adjusted with the difference between the two local ntp clocks.
int64_t now_ms = clock_->TimeInMilliseconds();
- int64_t ntp_offset = clock_->CurrentNtpInMilliseconds() - now_ms;
- int64_t receiver_capture_ntp_ms = receiver_capture_ms + ntp_offset;
+ int64_t offset_between_local_ntp_clocks =
+ clock_->CurrentNtpInMilliseconds() - now_ms - NtpOffsetMs();
+ receiver_capture_ntp_ms += offset_between_local_ntp_clocks;
if (now_ms - last_timing_log_ms_ > kTimingLogIntervalMs) {
RTC_LOG(LS_INFO) << "RTP timestamp: " << rtp_timestamp
<< " in NTP clock: " << sender_capture_ntp_ms
- << " estimated time in receiver clock: "
- << receiver_capture_ms
- << " converted to NTP clock: " << receiver_capture_ntp_ms;
+ << " estimated time in receiver NTP clock: "
+ << receiver_capture_ntp_ms;
last_timing_log_ms_ = now_ms;
}
return receiver_capture_ntp_ms;
}
+absl::optional<int64_t>
+RemoteNtpTimeEstimator::EstimateRemoteToLocalClockOffsetMs() {
+ if (ntp_clocks_offset_estimator_.GetNumberOfSamplesStored() <
+ kMinimumNumberOfSamples) {
+ return absl::nullopt;
+ }
+ return ntp_clocks_offset_estimator_.GetFilteredValue();
+}
+
} // namespace webrtc
diff --git a/modules/rtp_rtcp/source/remote_ntp_time_estimator_unittest.cc b/modules/rtp_rtcp/source/remote_ntp_time_estimator_unittest.cc
index c9b9434d..85f0848 100644
--- a/modules/rtp_rtcp/source/remote_ntp_time_estimator_unittest.cc
+++ b/modules/rtp_rtcp/source/remote_ntp_time_estimator_unittest.cc
@@ -9,17 +9,21 @@
*/
#include "modules/rtp_rtcp/include/remote_ntp_time_estimator.h"
-
+#include "absl/types/optional.h"
+#include "modules/rtp_rtcp/source/time_util.h"
#include "system_wrappers/include/clock.h"
+#include "system_wrappers/include/ntp_time.h"
#include "test/gmock.h"
#include "test/gtest.h"
namespace webrtc {
-static const int64_t kTestRtt = 10;
-static const int64_t kLocalClockInitialTimeMs = 123;
-static const int64_t kRemoteClockInitialTimeMs = 345;
-static const uint32_t kTimestampOffset = 567;
+constexpr int64_t kTestRtt = 10;
+constexpr int64_t kLocalClockInitialTimeMs = 123;
+constexpr int64_t kRemoteClockInitialTimeMs = 345;
+constexpr uint32_t kTimestampOffset = 567;
+constexpr int64_t kRemoteToLocalClockOffsetMs =
+ kLocalClockInitialTimeMs - kRemoteClockInitialTimeMs;
class RemoteNtpTimeEstimatorTest : public ::testing::Test {
protected:
@@ -39,9 +43,13 @@
kTimestampOffset;
}
+ NtpTime GetRemoteNtpTime() {
+ return TimeMicrosToNtp(remote_clock_.TimeInMicroseconds());
+ }
+
void SendRtcpSr() {
uint32_t rtcp_timestamp = GetRemoteTimestamp();
- NtpTime ntp = remote_clock_.CurrentNtpTime();
+ NtpTime ntp = GetRemoteNtpTime();
AdvanceTimeMilliseconds(kTestRtt / 2);
ReceiveRtcpSr(kTestRtt, rtcp_timestamp, ntp.seconds(), ntp.fractions());
@@ -53,7 +61,7 @@
int64_t ntp_error_fractions =
ntp_error_ms * static_cast<int64_t>(NtpTime::kFractionsPerSecond) /
1000;
- NtpTime ntp(static_cast<uint64_t>(remote_clock_.CurrentNtpTime()) +
+ NtpTime ntp(static_cast<uint64_t>(GetRemoteNtpTime()) +
ntp_error_fractions);
AdvanceTimeMilliseconds(kTestRtt / 2 + networking_delay_ms);
ReceiveRtcpSr(kTestRtt, rtcp_timestamp, ntp.seconds(), ntp.fractions());
@@ -96,6 +104,7 @@
// Local peer needs at least 2 RTCP SR to calculate the capture time.
const int64_t kNotEnoughRtcpSr = -1;
EXPECT_EQ(kNotEnoughRtcpSr, estimator_->Estimate(rtp_timestamp));
+ EXPECT_EQ(absl::nullopt, estimator_->EstimateRemoteToLocalClockOffsetMs());
AdvanceTimeMilliseconds(800);
// Remote sends second RTCP SR.
@@ -103,36 +112,24 @@
// Local peer gets enough RTCP SR to calculate the capture time.
EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
+ EXPECT_EQ(kRemoteToLocalClockOffsetMs,
+ estimator_->EstimateRemoteToLocalClockOffsetMs());
}
TEST_F(RemoteNtpTimeEstimatorTest, AveragesErrorsOut) {
// Remote peer sends first 10 RTCP SR without errors.
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
- AdvanceTimeMilliseconds(1000);
- SendRtcpSr();
+ for (int i = 0; i < 10; ++i) {
+ AdvanceTimeMilliseconds(1000);
+ SendRtcpSr();
+ }
AdvanceTimeMilliseconds(150);
uint32_t rtp_timestamp = GetRemoteTimestamp();
int64_t capture_ntp_time_ms = local_clock_.CurrentNtpInMilliseconds();
// Local peer gets enough RTCP SR to calculate the capture time.
EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
+ EXPECT_EQ(kRemoteToLocalClockOffsetMs,
+ estimator_->EstimateRemoteToLocalClockOffsetMs());
// Remote sends corrupted RTCP SRs
AdvanceTimeMilliseconds(1000);
@@ -147,6 +144,8 @@
// Errors should be averaged out.
EXPECT_EQ(capture_ntp_time_ms, estimator_->Estimate(rtp_timestamp));
+ EXPECT_EQ(kRemoteToLocalClockOffsetMs,
+ estimator_->EstimateRemoteToLocalClockOffsetMs());
}
} // namespace webrtc