Add sanity check for decreasing RTP timestamp in RtpToNtpMs. The capture time for a frame (capture_ms) is set later (in ViEEncoder::IncomingCapturedFrame) than the timestamp. Could potentially cause the RTP timestamp in consecutive RTCP SR to decrease. Example: // Frame1 46371: timestamp:2732, capture_ms:46373, rtcp SR ms: 46423 -> estimated current RTP timestamp:2732+(46423-46373)*90 = 7232 // Frame2 46404: timestamp:5702, capture_ms:46412, rtcp SR ms: 46428 -> estimated current RTP timestamp:5702+(46428-46412)*90 = 7142 // Diff: 33 ms: 33 ms, 39 ms, 5 ms BUG=b/31154867 Review-Url: https://codereview.webrtc.org/2354843003 Cr-Commit-Position: refs/heads/master@{#14454}

diff --git a/webrtc/system_wrappers/source/rtp_to_ntp.cc b/webrtc/system_wrappers/source/rtp_to_ntp.cc
index 6504737..0509146 100644
--- a/webrtc/system_wrappers/source/rtp_to_ntp.cc
+++ b/webrtc/system_wrappers/source/rtp_to_ntp.cc

@@ -110,6 +110,9 @@
                                &rtcp_timestamp_new)) {
     return false;
   }
+  if (rtcp_timestamp_new < rtcp_timestamp_old)
+    return false;
+
   double freq_khz;
   if (!CalculateFrequency(rtcp_ntp_ms_new,
                           rtcp_timestamp_new,

diff --git a/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc b/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
index 0e81e4d8..ce1f26d 100644
--- a/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
+++ b/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc

@@ -136,6 +136,20 @@
   EXPECT_FALSE(RtpToNtpMs(timestamp, rtcp, &timestamp_in_ms));
 }
 
+TEST(RtpToNtpTests, FailsForDecreasingRtpTimestamp) {
+  const uint32_t kNtpSec1 = 3683354930;
+  const uint32_t kNtpFrac1 = 699925050;
+  const uint32_t kTimestamp1 = 2192705742;
+  const uint32_t kNtpSec2 = kNtpSec1;
+  const uint32_t kNtpFrac2 = kNtpFrac1 + kOneMsInNtpFrac;
+  const uint32_t kTimestamp2 = kTimestamp1 - kTimestampTicksPerMs;
+  RtcpList rtcp;
+  rtcp.push_front(RtcpMeasurement(kNtpSec1, kNtpFrac1, kTimestamp1));
+  rtcp.push_front(RtcpMeasurement(kNtpSec2, kNtpFrac2, kTimestamp2));
+  int64_t timestamp_in_ms = -1;
+  EXPECT_FALSE(RtpToNtpMs(kTimestamp1, rtcp, &timestamp_in_ms));
+}
+
 TEST(UpdateRtcpListTests, InjectRtcpSrWithEqualNtp) {
   RtcpList rtcp;
   uint32_t ntp_sec = 0;