Advance picture id of keyframe if the stream has been continuous without a new keyframe for a while.

webrtc/modules/video_coding/rtp_frame_reference_finder.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 94 matching lines @@
 
   // While there still are padding packets and those padding packets are
   // continuous, then advance the "last-picture-id-with-padding" and remove
   // the stashed padding packet.
   while (padding_seq_num_it != stashed_padding_.end() &&
          *padding_seq_num_it == next_seq_num_with_padding) {
     gop_seq_num_it->second.second = next_seq_num_with_padding;
     ++next_seq_num_with_padding;
     padding_seq_num_it = stashed_padding_.erase(padding_seq_num_it);
   }
+
+  // In the case where the stream has been continuous without any new keyframes
+  // for a while there is a risk that new frames will appear to be older than
+  // the keyframe they belong to due to wrapping sequence number. In order
+  // to prevent this we advance the picture id of the keyframe every so often.
+  if (ForwardDiff(gop_seq_num_it->first, seq_num) > 10000) {
+    RTC_DCHECK_EQ(1ul, last_seq_num_gop_.size());
+    last_seq_num_gop_[seq_num] = gop_seq_num_it->second;
+    last_seq_num_gop_.erase(gop_seq_num_it);
+  }
 }
 
 void RtpFrameReferenceFinder::RetryStashedFrames() {
   size_t num_stashed_frames = stashed_frames_.size();
 
   // Clean up stashed frames if there are too many.
   while (stashed_frames_.size() > kMaxStashedFrames)
     stashed_frames_.pop_front();
 
   // Since frames are stashed if there is not enough data to determine their
@@ skipping 32 matching lines @@
 
   // We have received a frame but not yet a keyframe, stash this frame.
   if (last_seq_num_gop_.empty()) {
     stashed_frames_.push_back(std::move(frame));
     return;
   }
 
   // Clean up info for old keyframes but make sure to keep info
   // for the last keyframe.
   auto clean_to = last_seq_num_gop_.lower_bound(frame->last_seq_num() - 100);
-  if (clean_to != last_seq_num_gop_.end())
-    last_seq_num_gop_.erase(last_seq_num_gop_.begin(), clean_to);
+  for (auto it = last_seq_num_gop_.begin();
+       it != clean_to && last_seq_num_gop_.size() > 1;) {
+    it = last_seq_num_gop_.erase(it);
+  }
 
   // Find the last sequence number of the last frame for the keyframe
   // that this frame indirectly references.
   auto seq_num_it = last_seq_num_gop_.upper_bound(frame->last_seq_num());
   if (seq_num_it == last_seq_num_gop_.begin()) {
     LOG(LS_WARNING) << "Generic frame with packet range ["
                     << frame->first_seq_num() << ", " << frame->last_seq_num()
-                    << "] has no Gop, dropping frame.";
+                    << "] has no GoP, dropping frame.";
     return;
   }
   seq_num_it--;
 
   // Make sure the packet sequence numbers are continuous, otherwise stash
   // this frame.
   uint16_t last_picture_id_gop = seq_num_it->second.first;
   uint16_t last_picture_id_with_padding_gop = seq_num_it->second.second;
   if (frame->frame_type() == kVideoFrameDelta) {
     uint16_t prev_seq_num = frame->first_seq_num() - 1;
@@ skipping 542 matching lines @@
     if (!gof_info_.empty() &&
         AheadOf<uint8_t>(gof_info_.begin()->first, fixed_tl0)) {
       return true;
     }
   }
   return false;
 }
 
 }  // namespace video_coding
 }  // namespace webrtc