Add warning about timestamp non-monotonicity in the frame buffer.

webrtc/modules/video_coding/frame_buffer2.cc

Index: webrtc/modules/video_coding/frame_buffer2.cc
diff --git a/webrtc/modules/video_coding/frame_buffer2.cc b/webrtc/modules/video_coding/frame_buffer2.cc
index acc1bb83c5a0e448e030d42b98eab5d25315b0a1..451ea5cdf39bc38555f3cf81acafbb8c13ea3eda 100644
--- a/webrtc/modules/video_coding/frame_buffer2.cc
+++ b/webrtc/modules/video_coding/frame_buffer2.cc
@@ -144,6 +144,18 @@ FrameBuffer::ReturnReason FrameBuffer::NextFrame(
 
       PropagateDecodability(next_frame_it_->second);
       AdvanceLastDecodedFrame(next_frame_it_);
+      if (last_decoded_frame_it_ != frames_.end() &&
+          AheadOrAt(last_decoded_frame_timestamp_, frame->timestamp)) {

[brandtr, 2017/04/26 11:26:33]

This is correct being >=, right? I don't think we ever want to send the same
timestamp to the decoder more than once?

[philipel, 2017/04/26 12:27:28]

When we use SVC we will send frame with the same timestamp to the decoder.

What you can do is to check if we send a frame with the same timestamp as the
last frame and (last_decoded_frame_it_->first < key), then we know that this
frame is just a higher spatial layer frame in a superframe.

[brandtr, 2017/04/26 15:16:21]

Right. What about this?

+        int last_decoded_frame_picture_id =
+            last_decoded_frame_it_->first.picture_id;
+        LOG(LS_WARNING) << "Sending frame "
+                        << "(timestamp = " << frame->timestamp
+                        << ", picture_id = " << frame->picture_id
+                        << ") to decoder when last decoded frame was "
+                        << "(timestamp = " << last_decoded_frame_timestamp_
+                        << ", picture_id = " << last_decoded_frame_picture_id
+                        << ").";
+      }
       last_decoded_frame_timestamp_ = frame->timestamp;
       *frame_out = std::move(frame);
       return kFrameFound;