Reset frame timestamp epoch for new capturers.

talk/media/webrtc/webrtcvideoengine2.cc

 /*
  * libjingle
  * Copyright 2014 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 1765 matching lines @@
 bool WebRtcVideoChannel2::WebRtcVideoSendStream::SetCapturer(
     VideoCapturer* capturer) {
   TRACE_EVENT0("webrtc", "WebRtcVideoSendStream::SetCapturer");
   if (!DisconnectCapturer() && capturer == NULL) {
     return false;
   }
 
   {
     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.";
         webrtc::VideoFrame black_frame;
 
         CreateBlackFrame(&black_frame, last_dimensions_.width,
                          last_dimensions_.height);
 
         // Force this black frame not to be dropped due to timestamp order
         // check. As IncomingCapturedFrame will drop the frame if this frame's
@@ skipping 843 matching lines @@
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VIDEO