Decouple capture timestamp and reference time

content/browser/media/capture/desktop_capture_device.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/media/capture/desktop_capture_device.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
 #include <utility>
@@ skipping 108 matching lines @@
   // True when waiting for |desktop_capturer_| to capture current frame.
   bool capture_in_progress_;
 
   // True if the first capture call has returned. Used to log the first capture
   // result.
   bool first_capture_returned_;
 
   // The type of the capturer.
   DesktopMediaID::Type capturer_type_;
 
+  // The system time when we receive the first frame.
+  base::TimeTicks first_ref_time_;
+
   std::unique_ptr<webrtc::BasicDesktopFrame> black_frame_;
 
   // TODO(jiayl): Remove power_save_blocker_ when there is an API to keep the
   // screen from sleeping for the drive-by web.
   std::unique_ptr<PowerSaveBlocker> power_save_blocker_;
 
   DISALLOW_COPY_AND_ASSIGN(Core);
 };
 
 DesktopCaptureDevice::Core::Core(
@@ skipping 162 matching lines @@
         *frame,
         webrtc::DesktopVector(),
         webrtc::DesktopRect::MakeSize(frame->size()));
     output_data = output_frame_->data();
   } else {
     // If the captured frame matches the output size, we can return the pixel
     // data directly.
     output_data = frame->data();
   }
 
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (first_ref_time_.is_null())
+    first_ref_time_ = now;
   client_->OnIncomingCapturedData(
       output_data, output_bytes,
       media::VideoCaptureFormat(
           gfx::Size(output_size.width(), output_size.height()),
           requested_frame_rate_, media::PIXEL_FORMAT_ARGB),
-      0, base::TimeTicks::Now());
+      0, now, now - first_ref_time_);
 }
 
 void DesktopCaptureDevice::Core::OnCaptureTimer() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   if (!client_)
     return;
 
   CaptureFrameAndScheduleNext();
 }
@@ skipping 122 matching lines @@
 #else
   base::MessageLoop::Type thread_type = base::MessageLoop::TYPE_DEFAULT;
 #endif
 
   thread_.StartWithOptions(base::Thread::Options(thread_type, 0));
 
   core_.reset(new Core(thread_.task_runner(), std::move(capturer), type));
 }
 
 }  // namespace content