Send empty video frames when screen is not changing.

remoting/host/video_scheduler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/host/video_scheduler.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 13 matching lines @@
 #include "third_party/webrtc/modules/desktop_capture/desktop_frame.h"
 #include "third_party/webrtc/modules/desktop_capture/mouse_cursor.h"
 #include "third_party/webrtc/modules/desktop_capture/mouse_cursor_shape.h"
 
 namespace remoting {
 
 // Maximum number of frames that can be processed simultaneously.
 // TODO(hclam): Move this value to CaptureScheduler.
 static const int kMaxPendingFrames = 2;
 
-// Interval between empty keep-alive frames. These frames are sent only
-// when there are no real video frames being sent. To prevent PseudoTCP from
-// resetting congestion window this value must be smaller than the minimum
-// RTO used in PseudoTCP, which is 250ms.
+// Interval between empty keep-alive frames. These frames are sent only when the
+// stream is paused or inactive for some other reason (e.g. when blocked on
+// capturer). To prevent PseudoTCP from resetting congestion window this value
+// must be smaller than the minimum RTO used in PseudoTCP, which is 250ms.
 static const int kKeepAlivePacketIntervalMs = 200;
 
 static bool g_enable_timestamps = false;
 
 // static
 void VideoScheduler::EnableTimestampsForTests() {
   g_enable_timestamps = true;
 }
 
 VideoScheduler::VideoScheduler(
@@ skipping 319 matching lines @@
 }
 
 // Encoder thread --------------------------------------------------------------
 
 void VideoScheduler::EncodeFrame(
     scoped_ptr<webrtc::DesktopFrame> frame,
     int64 sequence_number,
     base::TimeTicks timestamp) {
   DCHECK(encode_task_runner_->BelongsToCurrentThread());
 
-  // Drop the frame if there were no changes.
+  // If there is nothing to encode then send an empty packet.
   if (!frame || frame->updated_region().is_empty()) {
     capture_task_runner_->DeleteSoon(FROM_HERE, frame.release());
-    capture_task_runner_->PostTask(
-        FROM_HERE, base::Bind(&VideoScheduler::FrameCaptureCompleted, this));
+    scoped_ptr<VideoPacket> packet(new VideoPacket());
+    packet->set_client_sequence_number(sequence_number);
+    network_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(
+            &VideoScheduler::SendVideoPacket, this, base::Passed(&packet)));
     return;
   }
 
   scoped_ptr<VideoPacket> packet = encoder_->Encode(*frame);
   packet->set_client_sequence_number(sequence_number);
 
   if (g_enable_timestamps) {
     packet->set_timestamp(timestamp.ToInternalValue());
   }
 
   // Destroy the frame before sending |packet| because SendVideoPacket() may
   // trigger another frame to be captured, and the screen capturer expects the
   // old frame to be freed by then.
   frame.reset();
 
   scheduler_.RecordEncodeTime(
       base::TimeDelta::FromMilliseconds(packet->encode_time_ms()));
   network_task_runner_->PostTask(
       FROM_HERE, base::Bind(&VideoScheduler::SendVideoPacket, this,
                             base::Passed(&packet)));
 }
 
 }  // namespace remoting