Decouple capture timestamp and reference time

media/capture/video/mac/video_capture_device_decklink_mac.mm

Index: media/capture/video/mac/video_capture_device_decklink_mac.mm
diff --git a/media/capture/video/mac/video_capture_device_decklink_mac.mm b/media/capture/video/mac/video_capture_device_decklink_mac.mm
index b075c4b234a28f790f63820a589398d4cb4619f4..cdb720b09d03ad969bdcdeeaf879ece3b9918f9c 100644
--- a/media/capture/video/mac/video_capture_device_decklink_mac.mm
+++ b/media/capture/video/mac/video_capture_device_decklink_mac.mm
@@ -92,6 +92,8 @@ class DeckLinkCaptureDelegate
   // |decklink_| represents a physical device attached to the host.
   ScopedDeckLinkPtr<IDeckLink> decklink_;
 
+  base::TimeTicks first_ref_time_;
+
   // Checks for Device (a.k.a. Audio) thread.
   base::ThreadChecker thread_checker_;
 
@@ -258,11 +260,14 @@ HRESULT DeckLinkCaptureDelegate::VideoInputFrameArrived(
       pixel_format);
   base::AutoLock lock(lock_);
   if (frame_receiver_) {
+    base::TimeTicks now = base::TimeTicks::Now();

[miu, 2016/05/18 22:35:40]

The call to TimeTicks::Now() should be moved to the top of the method (the
current thread might block waiting to acquire the |lock_|).

[qiangchen, 2016/05/20 17:55:14]

Done.

+    if (first_ref_time_.is_null())
+      first_ref_time_ = now;

[miu, 2016/05/18 22:35:40]

BTW--You can get the timestamp from the |video_frame| argument:

    const BMDTimeScale micros_time_scale = base::Time::kMicrosecondsPerSecond;
    BMDTimeValue frame_time;
    BMDTimeValue frame_duration;
    base::TimeDelta timestamp;
    if (SUCCEEDED(video_frame->GetStreamTime(&frame_time, &frame_duration,
micros_time_scale))) {
      timestamp = base::TimeDelta::FromMicroseconds(frame_time);
    } else {
      timestamp = now - first_ref_time_;
    }

[qiangchen, 2016/05/20 17:55:14]

Done.

     frame_receiver_->OnIncomingCapturedData(
         video_data, video_frame->GetRowBytes() * video_frame->GetHeight(),
         capture_format,
         0,  // Rotation.
-        base::TimeTicks::Now());
+        now, now - first_ref_time_);
   }
   return S_OK;
 }
@@ -451,11 +456,12 @@ void VideoCaptureDeviceDeckLinkMac::OnIncomingCapturedData(
     size_t length,
     const VideoCaptureFormat& frame_format,
     int rotation,  // Clockwise.
-    base::TimeTicks timestamp) {
+    base::TimeTicks reference_time,
+    base::TimeDelta timestamp) {
   base::AutoLock lock(lock_);
   if (client_) {
     client_->OnIncomingCapturedData(data, length, frame_format, rotation,
-                                    timestamp);
+                                    reference_time, timestamp);
   }
 }