Request keyframe if too many packets are missing and NACK is disabled.

webrtc/modules/video_coding/main/source/jitter_buffer.cc

Index: webrtc/modules/video_coding/main/source/jitter_buffer.cc
diff --git a/webrtc/modules/video_coding/main/source/jitter_buffer.cc b/webrtc/modules/video_coding/main/source/jitter_buffer.cc
index 9156cc1a61dba45624bda8c73da4886fce71b242..e2424c5760eef90c6badf307c2923f076cf93278 100644
--- a/webrtc/modules/video_coding/main/source/jitter_buffer.cc
+++ b/webrtc/modules/video_coding/main/source/jitter_buffer.cc
@@ -643,7 +643,7 @@ VCMFrameBufferEnum VCMJitterBuffer::InsertPacket(const VCMPacket& packet,
       if (IsPacketRetransmitted(packet)) {
         frame->IncrementNackCount();
       }
-      if (!UpdateNackList(packet.seqNum) &&
+      if (!CoverSequenceUpTo(packet.seqNum) &&
           packet.frameType != kVideoFrameKey) {
         buffer_state = kFlushIndicator;
       }
@@ -939,10 +939,7 @@ VCMFrameBuffer* VCMJitterBuffer::NextFrame() const {
   return NULL;
 }
 
-bool VCMJitterBuffer::UpdateNackList(uint16_t sequence_number) {
-  if (nack_mode_ == kNoNack) {
-    return true;
-  }
+bool VCMJitterBuffer::CoverSequenceUpTo(uint16_t sequence_number) {
   // Make sure we don't add packets which are already too old to be decoded.
   if (!last_decoded_state_.in_initial_state()) {
     latest_received_sequence_number_ = LatestSequenceNumber(
@@ -951,6 +948,10 @@ bool VCMJitterBuffer::UpdateNackList(uint16_t sequence_number) {
   }
   if (IsNewerSequenceNumber(sequence_number,
                             latest_received_sequence_number_)) {
+    if (nack_mode_ == kNoNack) {
+      // Packets missing but NACK disabled, request key frame.

[stefan-webrtc, 2015/07/01 13:41:02]

This isn't a good way of handling lost packets since a lost packet doesn't
necessarily imply a decodable frame sequence.

Some decoders (vp8 and h.264) can decode frames with missing packets and damaged
references in a (sometimes) satisfactory way. Therefore we have traditionally
left the decision to request a key frame or not to the decoder (in non-NACK
mode, that is). Other ways than a key frame can also be used for the recovery of
a loss.

Some frame sequences may use layering to achieve robustness, so that for
instance base layer frames can be decoded even if higher layers are lost. This
solution will break that functionality when NACK is disabled.

See the other places in the code I commented on.

+      return false;
+    }
     // Push any missing sequence numbers to the NACK list.
     for (uint16_t i = latest_received_sequence_number_ + 1;
          IsNewerSequenceNumber(sequence_number, i); ++i) {
@@ -967,7 +968,7 @@ bool VCMJitterBuffer::UpdateNackList(uint16_t sequence_number) {
       LOG(LS_WARNING) << "Requesting key frame due to missing too old packets";
       return false;
     }
-  } else {
+  } else if (nack_mode_ != kNoNack) {
     missing_sequence_numbers_.erase(sequence_number);
     TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"), "RemoveNack",
                          "seqnum", sequence_number);