Only advance |first_seq_num_| if packets are explicitly cleared from the PacketBuffer.

webrtc/modules/video_coding/packet_buffer.h

 /*
  *  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 76 matching lines @@
     // If this packet has been used to create a frame already.
     bool frame_created = false;
   };
 
   Clock* const clock_;
 
   // Tries to expand the buffer.
   bool ExpandBufferSize() EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Test if all previous packets has arrived for the given sequence number.
-  bool IsContinuous(uint16_t seq_num) const EXCLUSIVE_LOCKS_REQUIRED(crit_);
+  bool PotentialNewFrame(uint16_t seq_num) const
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Test if all packets of a frame has arrived, and if so, creates a frame.
   // May create multiple frames per invocation.
   void FindFrames(uint16_t seq_num) EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Copy the bitstream for |frame| to |destination|.
   // Virtual for testing.
   virtual bool GetBitstream(const RtpFrameObject& frame, uint8_t* destination);
 
   // Get the packet with sequence number |seq_num|.
@@ skipping 12 matching lines @@
 
   // The fist sequence number currently in the buffer.
   uint16_t first_seq_num_ GUARDED_BY(crit_);
 
   // The last sequence number currently in the buffer.
   uint16_t last_seq_num_ GUARDED_BY(crit_);
 
   // If the packet buffer has received its first packet.
   bool first_packet_received_ GUARDED_BY(crit_);
 
+  // If the buffer is cleared to a specific packet.
+  bool has_cleared_to_ GUARDED_BY(crit_);

[stefan-webrtc, 2016/10/18 17:57:23]

I have a hard time understanding this member. What specific packet has it
cleared to?

[philipel, 2016/10/19 08:34:54]

This variable is set to true when ClearTo() has been called. The reason I have
this variable is to be able to know if I should drop a packet because it's old
(we have cleared past it), or if I should accept it (due to reordering that
might occur at the start of the stream). See line 68 in packet_buffer.cc.

[danilchap, 2016/10/19 09:25:10]

may be name it something like
is_cleared_before_first_seq_num_ :
instead of describing past action, describe current state. (is instead of
has/was/had)
incorporate seq_num it is cleared to into name.
'before' as a notion of '<' since 'to' might mean '<='

+
   // Buffer that holds the inserted packets.
   std::vector<VCMPacket> data_buffer_ GUARDED_BY(crit_);
 
   // Buffer that holds the information about which slot that is currently in use
   // and information needed to determine the continuity between packets.
   std::vector<ContinuityInfo> sequence_buffer_ GUARDED_BY(crit_);
 
   // Called when a received frame is found.
   OnReceivedFrameCallback* const received_frame_callback_;
 
   mutable volatile int ref_count_ = 0;
 };
 
 }  // namespace video_coding
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_PACKET_BUFFER_H_