Fix failed capture handling in WebrtcVideoStream

remoting/protocol/webrtc_frame_scheduler_simple.cc

 // Copyright 2016 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/protocol/webrtc_frame_scheduler_simple.h"
 
 #include <algorithm>
 
 #include "remoting/protocol/frame_stats.h"
 #include "remoting/protocol/webrtc_dummy_video_encoder.h"
@@ skipping 160 matching lines @@
   }
 }
 
 bool WebrtcFrameSchedulerSimple::OnFrameCaptured(
     const webrtc::DesktopFrame* frame,
     WebrtcVideoEncoder::FrameParams* params_out) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   base::TimeTicks now = base::TimeTicks::Now();
 
-  if ((!frame || frame->updated_region().is_empty()) && !top_off_is_active_ &&
-      !key_frame_request_) {
-    frame_pending_ = false;
-    ScheduleNextFrame(now);
-    return false;
+  if ((!frame || frame->updated_region().is_empty())) {
+    // If we've failed to capture a frame or captured an empty frame we still
+    // need to encode and send the previous frame when top-off is active or a
+    // key-frame was requested. But it makes sense only when we have a frame to
+    // send, i.e. there is nothing to send if first capture request failed.
+    bool resend_last_frame =
+        captured_first_frame_ && (top_off_is_active_ || key_frame_request_);

[Jamie, 2017/03/21 18:33:36]

Given the name of this variable, I would expect to see the |frame| replaced by
the previous frame here. In fact, this class doesn't even store the previous
frame, which makes me suspect that this isn't the right variable name. Where is
the resend-last-frame logic?

[Sergey Ulanov, 2017/03/21 19:40:26]

The encoder keeps current frame internally (in YUV). For every Encode() call it
updates the content of that buffer from the new frame by copying
updated_region() (while also performing RGB->YUV conversion) and then encodes
that buffer.
So encoder->Encode(nullptr) will return either top-off or key-frame (when the
corresponding flag is set).

+    if (!resend_last_frame) {
+      frame_pending_ = false;
+      ScheduleNextFrame(now);
+      return false;
+    }
   }
 
   if (frame) {
+    captured_first_frame_ = true;
     encoder_bitrate_.SetFrameSize(frame->size());
   }
 
   params_out->bitrate_kbps = encoder_bitrate_.GetTargetBitrateKbps();
   params_out->duration = kTargetFrameInterval;
   params_out->key_frame = key_frame_request_;
   key_frame_request_ = false;
 
   params_out->vpx_min_quantizer = 10;
 
@@ skipping 97 matching lines @@
 void WebrtcFrameSchedulerSimple::CaptureNextFrame() {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!frame_pending_);
   last_capture_started_time_ = base::TimeTicks::Now();
   frame_pending_ = true;
   capture_callback_.Run();
 }
 
 }  // namespace protocol
 }  // namespace remoting