Add Cast PLI support on sender side.

media/cast/sender/video_sender.cc

Index: media/cast/sender/video_sender.cc
diff --git a/media/cast/sender/video_sender.cc b/media/cast/sender/video_sender.cc
index 1c39ecbc786c8646b1d92a2262857839cf8348bf..fb753b8d8120b94b7736db7b6a91ec427f3ce88c 100644
--- a/media/cast/sender/video_sender.cc
+++ b/media/cast/sender/video_sender.cc
@@ -41,6 +41,12 @@ const int kConstantTimeMs = 75;
 // available to handle the occasional more-complex frames).
 const int kTargetUtilizationPercentage = 75;
 
+// This is the minimum duration between two key frame requests. Too many Key
+// frames will reduce the dependency among frames, but reduce the picture
+// quality as well.
+const base::TimeDelta kMinKeyFrameRequestDuration =

[miu, 2016/02/26 23:36:07]

Static initializer foo: In Chromium code, we can only use POD types for
constants.  So, this needs to become (with naming change, based on later
comments):

  const int kMinPliResolveIntervalMs = 500;

[xjz, 2016/02/27 05:53:32]

Done.

+    base::TimeDelta::FromMilliseconds(500);
+
 // Extract capture begin/end timestamps from |video_frame|'s metadata and log
 // it.
 void LogVideoCaptureTimestamps(CastEnvironment* cast_environment,
@@ -134,11 +140,11 @@ VideoSender::VideoSender(
   transport_config.aes_iv_mask = video_config.aes_iv_mask;
 
   transport_sender->InitializeVideo(
-      transport_config,
-      base::Bind(&VideoSender::OnReceivedCastFeedback,
-                 weak_factory_.GetWeakPtr()),
+      transport_config, base::Bind(&VideoSender::OnReceivedCastFeedback,
+                                   weak_factory_.GetWeakPtr()),
       base::Bind(&VideoSender::OnMeasuredRoundTripTime,
-                 weak_factory_.GetWeakPtr()));
+                 weak_factory_.GetWeakPtr()),
+      base::Bind(&VideoSender::OnReceivedPli, weak_factory_.GetWeakPtr()));
 }
 
 VideoSender::~VideoSender() {
@@ -154,6 +160,16 @@ void VideoSender::InsertRawVideoFrame(
     return;
   }
 
+  // Request a key frame when receive the PLI and it has been passed more than
+  // |kMinKeyFrameRequestDuration| frome encoding last key frame.
+  if (picture_lost_at_receiver_) {

[miu, 2016/02/26 23:36:07]

The client may call InsertRawVideoFrame() several times before
|last_encoded_key_frame_| is updated in OnEncodedVideoFrame().  That means we
would be making several redundant requests for key frames in the meantime.

Instead, what if the |last_encoded_key_frame_| timestamp became a
|last_attempt_to_resolve_picture_loss_| timestamp?  Then, the logic here would
look like:

  if (picture_lost_at_receiver_) {
    if (last_attempt_to_resolve_picture_loss_.is_null() ||
        ((reference_time -
last_attempt_to_resolve_picture_loss_).InMilliseconds() >
kMinPliResolveIntervalMs)) {
      video_encoder_->GenerateKeyFrame();
      last_attempt_to_resolve_picture_loss_ = reference_time;
    }
    // Note: |picture_lost_at_receiver_| is cleared in FrameSender
when...blahblahblah...
  }

Also, let's move all this down to line 210.  That ensures the reference_time is
valid (monotonically increasing), which is important for this logic to work
correctly.

[xjz, 2016/02/27 05:53:32]

Done.

+    base::TimeDelta duration;
+    if (last_encoded_key_frame_ != base::TimeTicks())
+      duration = reference_time - last_encoded_key_frame_;
+    if (duration > kMinKeyFrameRequestDuration)
+      video_encoder_->GenerateKeyFrame();
+  }
+
   const RtpTimeTicks rtp_timestamp =
       RtpTimeTicks::FromTimeDelta(video_frame->timestamp(), kVideoFrequency);
   LogVideoCaptureTimestamps(cast_environment_.get(), *video_frame,
@@ -306,6 +322,9 @@ void VideoSender::OnEncodedVideoFrame(
   frames_in_encoder_--;
   DCHECK_GE(frames_in_encoder_, 0);
 
+  if (encoded_frame->dependency == EncodedFrame::KEY)
+    last_encoded_key_frame_ = encoded_frame->reference_time;
+
   duration_in_encoder_ =
       last_enqueued_frame_reference_time_ - encoded_frame->reference_time;