Don't detect a new frame if a previous packet is used in a previous frame.

webrtc/modules/video_coding/packet_buffer.cc

Index: webrtc/modules/video_coding/packet_buffer.cc
diff --git a/webrtc/modules/video_coding/packet_buffer.cc b/webrtc/modules/video_coding/packet_buffer.cc
index 03aeb5a4a9691e7fd867aada0b97628e272fd71c..e68bf623a47947ec7abf1f9240cea0f258d2bcac 100644
--- a/webrtc/modules/video_coding/packet_buffer.cc
+++ b/webrtc/modules/video_coding/packet_buffer.cc
@@ -40,7 +40,6 @@ PacketBuffer::PacketBuffer(Clock* clock,
       size_(start_buffer_size),
       max_size_(max_buffer_size),
       first_seq_num_(0),
-      last_seq_num_(0),
       first_packet_received_(false),
       is_cleared_to_first_seq_num_(false),
       data_buffer_(start_buffer_size),
@@ -65,7 +64,6 @@ bool PacketBuffer::InsertPacket(VCMPacket* packet) {
 
     if (!first_packet_received_) {
       first_seq_num_ = seq_num;
-      last_seq_num_ = seq_num;
       first_packet_received_ = true;
     } else if (AheadOf(first_seq_num_, seq_num)) {
       // If we have explicitly cleared past this packet then it's old,
@@ -100,9 +98,6 @@ bool PacketBuffer::InsertPacket(VCMPacket* packet) {
       }
     }
 
-    if (AheadOf(seq_num, last_seq_num_))
-      last_seq_num_ = seq_num;
-
     sequence_buffer_[index].frame_begin = packet->isFirstPacket;
     sequence_buffer_[index].frame_end = packet->markerBit;
     sequence_buffer_[index].seq_num = packet->seqNum;
@@ -186,6 +181,8 @@ bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
     return true;
   if (!sequence_buffer_[prev_index].used)
     return false;
+  if (sequence_buffer_[prev_index].frame_created)

[stefan-webrtc, 2017/01/10 11:50:00]

It's not clear to me why this is needed. Why can't it be a new frame in this
case? Is it because the previous packet created a new frame, and this packet
doesn't have the frame_begin flag set?

I also don't follow how the test added would capture this... :)

[philipel, 2017/01/10 12:03:36]

This check covers this case:

p1:
 seqnum 1
 first true
 marker true

p2:
 seqnum 2
 first false
 marker true

When we receive p1 it will be correctly detected as a complete frame. When we
receive p2 it will check if the previous packet is continuous, which it is, and
then try to create a new frame since this is the last packet of the frame.

Without this fix then a frame containing p1 and p2 would be created, even though
p1 is already part of a frame. With this fix we detect that p1 is already part
of a frame and should not be used to create a new frame.

+    return false;
   if (sequence_buffer_[prev_index].seq_num !=
       sequence_buffer_[index].seq_num - 1) {
     return false;