Reset frame timestamp epoch for new capturers.

talk/media/webrtc/webrtcvideoengine2.cc

Index: talk/media/webrtc/webrtcvideoengine2.cc
diff --git a/talk/media/webrtc/webrtcvideoengine2.cc b/talk/media/webrtc/webrtcvideoengine2.cc
index a3f8b8e7acc75fa6d76b7398595ffdfc6673c827..c810b5b06871659c4984d2a4adb64ac5a0c59b93 100644
--- a/talk/media/webrtc/webrtcvideoengine2.cc
+++ b/talk/media/webrtc/webrtcvideoengine2.cc
@@ -1783,6 +1783,10 @@ bool WebRtcVideoChannel2::WebRtcVideoSendStream::SetCapturer(
   {
     rtc::CritScope cs(&lock_);
 
+    // Reset timestamps to realign new incoming frames to a webrtc timestamp. A
+    // new capturer may have a different timestamp delta than the previous one.
+    first_frame_timestamp_ms_ = 0;
+
     if (capturer == NULL) {
       if (stream_ != NULL) {
         LOG(LS_VERBOSE) << "Disabling capturer, sending black frame.";