Only create H264 frames if there are no gaps in the packet sequence number.

webrtc/modules/video_coding/packet_buffer.h

Index: webrtc/modules/video_coding/packet_buffer.h
diff --git a/webrtc/modules/video_coding/packet_buffer.h b/webrtc/modules/video_coding/packet_buffer.h
index 3d9eb9cb421515aeb4a8f48b13cecf8699b2817a..1018ac468a1049463b5edc7688823ac7d56dadef 100644
--- a/webrtc/modules/video_coding/packet_buffer.h
+++ b/webrtc/modules/video_coding/packet_buffer.h
@@ -11,8 +11,9 @@
 #ifndef WEBRTC_MODULES_VIDEO_CODING_PACKET_BUFFER_H_
 #define WEBRTC_MODULES_VIDEO_CODING_PACKET_BUFFER_H_
 
-#include <vector>
 #include <memory>
+#include <set>
+#include <vector>
 
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/scoped_ref_ptr.h"
@@ -54,6 +55,7 @@ class PacketBuffer {
   virtual bool InsertPacket(VCMPacket* packet);
   void ClearTo(uint16_t seq_num);
   void Clear();
+  void PaddingReceived(uint16_t seq_num);

[stefan-webrtc, 2017/06/07 11:39:17]

It can probably be discussed how important this is. We could perhaps decide not
to support padding in the same ssrc as an h.264 stream isn't allowed?

Maybe it's better to do it separately after a PSA...

[philipel, 2017/06/07 14:04:35]

I think we should make a PSA that only media packets will be allowed in the
media stream, so padding/FEC will always be sent on a separate SSRC.

 
   // Timestamp (not RTP timestamp) of the last received packet/keyframe packet.
   rtc::Optional<int64_t> LastReceivedPacketMs() const;
@@ -121,6 +123,8 @@ class PacketBuffer {
   // Virtual for testing.
   virtual void ReturnFrame(RtpFrameObject* frame);
 
+  void UpdateMissingPackets(uint16_t seq_num) EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
   rtc::CriticalSection crit_;
 
   // Buffer size_ and max_size_ must always be a power of two.
@@ -150,6 +154,10 @@ class PacketBuffer {
   rtc::Optional<int64_t> last_received_packet_ms_ GUARDED_BY(crit_);
   rtc::Optional<int64_t> last_received_keyframe_packet_ms_ GUARDED_BY(crit_);
 
+  rtc::Optional<uint16_t> last_inserted_seq_num_ GUARDED_BY(crit_);
+  std::set<uint16_t, DescendingSeqNumComp<uint16_t>> missing_packets_
+      GUARDED_BY(crit_);
+
   mutable volatile int ref_count_ = 0;
 };