Update screen simulcast config and fix periodic encoder param update

webrtc/video/vie_encoder.cc

Index: webrtc/video/vie_encoder.cc
diff --git a/webrtc/video/vie_encoder.cc b/webrtc/video/vie_encoder.cc
index aa5e593ed853ee47d05e712469f41691582a9742..a936740220499712df42f6df6a09106aab239c4a 100644
--- a/webrtc/video/vie_encoder.cc
+++ b/webrtc/video/vie_encoder.cc
@@ -676,8 +676,8 @@ void ViEEncoder::EncodeVideoFrame(const VideoFrame& video_frame,
                  vcm::VCMProcessTimer::kDefaultProcessIntervalMs) {
     video_sender_.UpdateChannelParemeters(rate_allocator_.get(),
                                           bitrate_observer_);
+    last_parameters_update_ms_.emplace(now_ms);
   }

[stefan-webrtc, 2017/04/05 15:06:48]

I don't immediately understand what the problem was here. Did we get in the
(missing) else clause? Should we not set last_parameters_update_ms_ if we run
ReconfigureEncoder()? After all, it does call
video_sender_.UpdateChannelParemeters().

[sprang_webrtc, 2017/05/08 08:50:53]

The intent for |last_parameters_update_ms_| is to indicate when we last called
video_sender_.UpdateChannelParemeters().
The second check above looks if more than one second has passed since last we
did that and if so we should update the encoder. The problem is that we now
reset that timestamp on every frame, so unless there is more than one second
between incoming frames that update will never be triggered.

It's true that ReconfigureEncoder() also updates the encoder, so if you want to
I can add an update to the timer there as well, but it's probably a rare
occasion so I don't the we risk updating the parameters too often...

[stefan-webrtc, 2017/05/08 11:09:40]

I don't know. Maybe it's good to be consistent? Otherwise I think we should
comment on why we don't set it, as it'll be very hard for someone new to the
code to understand this.

[sprang_webrtc, 2017/05/08 11:12:27]

Alright, added update after ReconfigureEncoder() as well.

-  last_parameters_update_ms_.emplace(now_ms);
 
   if (EncoderPaused()) {
     TraceFrameDropStart();