Padding is now used to check for continuity in the packet sequence.

webrtc/modules/video_coding/rtp_frame_reference_finder.h

Index: webrtc/modules/video_coding/rtp_frame_reference_finder.h
diff --git a/webrtc/modules/video_coding/rtp_frame_reference_finder.h b/webrtc/modules/video_coding/rtp_frame_reference_finder.h
index 5fd67ab2a4a69216db043cb296bbab902e2774bf..fd27d4458eed646215aca52e3f1370b67a0dfcf3 100644
--- a/webrtc/modules/video_coding/rtp_frame_reference_finder.h
+++ b/webrtc/modules/video_coding/rtp_frame_reference_finder.h
@@ -33,6 +33,7 @@ class RtpFrameReferenceFinder {
  public:
   explicit RtpFrameReferenceFinder(OnCompleteFrameCallback* frame_callback);
   void ManageFrame(std::unique_ptr<RtpFrameObject> frame);
+  void PaddingReceived(uint16_t seq_num);
 
  private:
   static const uint16_t kPicIdLength = 1 << 7;
@@ -41,9 +42,15 @@ class RtpFrameReferenceFinder {
   static const int kMaxStashedFrames = 10;
   static const int kMaxNotYetReceivedFrames = 20;
   static const int kMaxGofSaved = 15;
+  static const int kMaxPaddingAge = 100;
 
   rtc::CriticalSection crit_;
 
+  // Find the relevant group of pictures and update its "last-picture-id-with
+  // padding" sequence number.
+  void UpdateLastPictureIdWithPadding(uint16_t seq_num)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
   // Retry finding references for all frames that previously didn't have
   // all information needed.
   void RetryStashedFrames() EXCLUSIVE_LOCKS_REQUIRED(crit_);
@@ -93,15 +100,25 @@ class RtpFrameReferenceFinder {
   // All picture ids are unwrapped to 16 bits.
   uint16_t UnwrapPictureId(uint16_t picture_id) EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
-  // Holds the last sequence number of the last frame that has been created
-  // given the last sequence number of a given keyframe.
-  std::map<uint16_t, uint16_t, DescendingSeqNumComp<uint16_t>> last_seq_num_gop_
-      GUARDED_BY(crit_);
+
+  // For every group of pictures, hold two sequence numbers. The first being
+  // the sequence number of the last packet of the last completed frame, and
+  // the second being the sequence number of the last packet of the last
+  // completed frame advanced by any potential continuous packets of padding.
+  std::map<uint16_t,
+           std::pair<uint16_t, uint16_t>,
+           DescendingSeqNumComp<uint16_t>>
+      last_seq_num_gop_ GUARDED_BY(crit_);
 
   // Save the last picture id in order to detect when there is a gap in frames
   // that have not yet been fully received.
   int last_picture_id_ GUARDED_BY(crit_);
 
+  // Padding packets that have been received but that is not yet continuous with

[stefan-webrtc, 2016/07/05 08:00:40]

"...but that are not..."

[philipel, 2016/07/05 08:41:01]

Done.

+  // any group of pictures.
+  std::set<uint16_t, DescendingSeqNumComp<uint16_t>> received_padding_

[stefan-webrtc, 2016/07/05 08:00:40]

Maybe call these stashed_padding_ to make it more clear that they are stored
here until they can be inserted in their right position? Btw, is it necessary to
keep stashed padding separate from stashed regular packets?

[philipel, 2016/07/05 08:41:01]

Done.
This is the only place we stash packets in the RtpFrameReferenceFinder class.

+      GUARDED_BY(crit_);
+
   // The last unwrapped picture id. Used to unwrap the picture id from a length
   // of |kPicIdLength| to 16 bits.
   int last_unwrap_ GUARDED_BY(crit_);