Use microsecond timestamp in cricket::VideoFrame.

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index ec6b033d2f7a3862be69a9c25390d646968cfd2c..0471870e52045c4aa8149dcb7e90e42e089b9596 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -1514,7 +1514,7 @@ WebRtcVideoChannel2::WebRtcVideoSendStream::WebRtcVideoSendStream(
       pending_encoder_reconfiguration_(false),
       allocated_encoder_(nullptr, webrtc::kVideoCodecUnknown, false),
       sending_(false),
-      first_frame_timestamp_ms_(0),
+      first_frame_timestamp_valid_(false),

[perkj_webrtc, 2016/04/13 05:57:06]

why this change? 

[nisse-webrtc, 2016/04/13 06:54:50]

Zero is a valid timestamp offset, we need a separate flag to tell if the offset
has been set yet or not.

[pbos-webrtc, 2016/04/13 09:56:24]

Sounds like we should use rtc::Optional then, or agree to not use rtc::Optional
elsewhere, it feels weird to mix styles in this code.

[nisse-webrtc, 2016/04/13 11:30:47]

Done. Is it correct to rely on the default constructor, to initialize it to
"unset"?

       last_frame_timestamp_ms_(0) {
   parameters_.config.rtp.max_packet_size = kVideoMtu;
   parameters_.conference_mode = send_params.conference_mode;
@@ -1573,12 +1573,15 @@ void WebRtcVideoChannel2::WebRtcVideoSendStream::OnFrame(
   }
 
   int64_t frame_delta_ms = frame.GetTimeStamp() / rtc::kNumNanosecsPerMillisec;
+
   // frame->GetTimeStamp() is essentially a delta, align to webrtc time
-  if (first_frame_timestamp_ms_ == 0) {
+  if (!first_frame_timestamp_valid_) {
     first_frame_timestamp_ms_ = rtc::Time() - frame_delta_ms;
+    first_frame_timestamp_valid_ = true;
   }
 
   last_frame_timestamp_ms_ = first_frame_timestamp_ms_ + frame_delta_ms;
+
   video_frame.set_render_time_ms(last_frame_timestamp_ms_);
   // Reconfigure codec if necessary.
   SetDimensions(video_frame.width(), video_frame.height());
@@ -1608,7 +1611,7 @@ void WebRtcVideoChannel2::WebRtcVideoSendStream::SetSource(
 
     // 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;
+    first_frame_timestamp_valid_ = false;
 
     if (source == NULL) {
       if (stream_ != NULL) {