[video-raf] Fix capture time for remote video sources

Set capture time to the NTP timestamp of the video frame
for remote video sources. Compensate for NTP offset.

Bug: 1011581
Change-Id: I75916d53503141bab7fd88cebe52c4aee83652fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095007Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Johannes Kron <kron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749133}

third_party/blink/renderer/modules/peerconnection/media_stream_remote_video_source.cc

@@ -25,7 +25,8 @@
 #include "third_party/blink/renderer/platform/wtf/thread_safe_ref_counted.h"
 #include "third_party/webrtc/api/video/i420_buffer.h"
 #include "third_party/webrtc/api/video/recordable_encoded_frame.h"
-#include "third_party/webrtc/rtc_base/time_utils.h"  // for TimeMicros
+#include "third_party/webrtc/rtc_base/time_utils.h"
+#include "third_party/webrtc/system_wrappers/include/clock.h"
 
 namespace WTF {
 
@@ -145,6 +146,12 @@ class MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate
 
   // WebRTC Chromium timestamp diff
   const base::TimeDelta time_diff_encoded_;
+
+  // WebRTC real time clock, needed to determine NTP offset.
+  webrtc::Clock* clock_;
+
+  // Offset between NTP clock and WebRTC clock.
+  const int64_t ntp_offset_;
 };
 
 MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::
@@ -163,11 +170,13 @@ MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::
                  base::TimeDelta::FromMicroseconds(rtc::TimeMicros())),
       start_timestamp_encoded_(media::kNoTimestamp),
       time_diff_encoded_(base::TimeTicks::Now() - base::TimeTicks() -
-                         base::TimeDelta::FromMicroseconds(rtc::TimeMicros())) {
-}
+                         base::TimeDelta::FromMicroseconds(rtc::TimeMicros())),
+      clock_(webrtc::Clock::GetRealTimeClock()),
+      ntp_offset_(clock_->TimeInMilliseconds() -
+                  clock_->CurrentNtpInMilliseconds()) {}
 
 MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::
-    ~RemoteVideoSourceDelegate() {}
+    ~RemoteVideoSourceDelegate() = default;
 
 void MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::OnFrame(
     const webrtc::VideoFrame& incoming_frame) {
@@ -301,10 +310,11 @@ void MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::OnFrame(
 
   // Set capture time to the NTP time, which is the estimated capture time
   // converted to the local clock.
-  if (incoming_frame.ntp_time_ms() != 0) {
+  if (incoming_frame.ntp_time_ms() > 0) {
     const base::TimeTicks capture_time =
         base::TimeTicks() +
-        base::TimeDelta::FromMilliseconds(incoming_frame.ntp_time_ms()) +
+        base::TimeDelta::FromMilliseconds(incoming_frame.ntp_time_ms() +
+                                          ntp_offset_) +
         time_diff_;
     video_frame->metadata()->SetTimeTicks(
         media::VideoFrameMetadata::CAPTURE_BEGIN_TIME, capture_time);

third_party/blink/renderer/modules/peerconnection/media_stream_remote_video_source_test.cc

@@ -28,6 +28,7 @@
 #include "third_party/webrtc/api/rtp_packet_infos.h"
 #include "third_party/webrtc/api/video/color_space.h"
 #include "third_party/webrtc/api/video/i420_buffer.h"
+#include "third_party/webrtc/system_wrappers/include/clock.h"
 #include "ui/gfx/color_space.h"
 
 namespace blink {
@@ -327,6 +328,11 @@ TEST_F(MediaStreamRemoteVideoSourceTest,
       kProcessingFinish - webrtc::TimeDelta::Millis(1.0e3 * kProcessingTime);
   const webrtc::Timestamp kCaptureTime =
       kProcessingStart - webrtc::TimeDelta::Millis(20.0);
+  webrtc::Clock* clock = webrtc::Clock::GetRealTimeClock();
+  const int64_t ntp_offset =
+      clock->CurrentNtpInMilliseconds() - clock->TimeInMilliseconds();
+  const webrtc::Timestamp kCaptureTimeNtp =
+      kCaptureTime + webrtc::TimeDelta::Millis(ntp_offset);
   // Expected capture time in Chromium epoch.
   base::TimeTicks kExpectedCaptureTime =
       base::TimeTicks() + base::TimeDelta::FromMilliseconds(kCaptureTime.ms()) +
@@ -348,7 +354,7 @@ TEST_F(MediaStreamRemoteVideoSourceTest,
       webrtc::VideoFrame::Builder()
           .set_video_frame_buffer(buffer)
           .set_timestamp_rtp(kRtpTimestamp)
-          .set_ntp_time_ms(kCaptureTime.ms())
+          .set_ntp_time_ms(kCaptureTimeNtp.ms())
           .set_packet_infos(webrtc::RtpPacketInfos(packet_infos))
           .build();