Reland of Only compare sequence numbers from the same SSRC in ForwardErrorCorrection.

webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc

 /*
  *  Copyright (c) 2012 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 31 matching lines @@
 // The range is between 0 and 255, where 255 corresponds to 100% overhead
 // (relative to the number of protected media packets).
 constexpr uint8_t kHighProtectionThreshold = 80;
 
 // This threshold is used to adapt the |kMinMediaPackets| threshold, based
 // on the average number of packets per frame seen so far. When there are few
 // packets per frame (as given by this threshold), at least
 // |kMinMediaPackets| + 1 packets are sent to the FEC code.
 constexpr float kMinMediaPacketsAdaptationThreshold = 2.0f;
 
+// At construction time, we don't know the SSRC that is used for the generated
+// FEC packets, but we still need to give it to the ForwardErrorCorrection ctor
+// to be used in the decoding.
+// TODO(brandtr): Get rid of this awkwardness by splitting
+// ForwardErrorCorrection in two objects -- one encoder and one decoder.
+constexpr uint32_t kUnknownSsrc = 0;
+
 }  // namespace
 
 RedPacket::RedPacket(size_t length)
     : data_(new uint8_t[length]), length_(length), header_length_(0) {}
 
 void RedPacket::CreateHeader(const uint8_t* rtp_header,
                              size_t header_length,
                              int red_payload_type,
                              int payload_type) {
   RTC_DCHECK_LE(header_length + kRedForFecHeaderLength, length_);
@@ skipping 25 matching lines @@
 
 uint8_t* RedPacket::data() const {
   return data_.get();
 }
 
 size_t RedPacket::length() const {
   return length_;
 }
 
 UlpfecGenerator::UlpfecGenerator()
-    : UlpfecGenerator(ForwardErrorCorrection::CreateUlpfec()) {}
+    : UlpfecGenerator(ForwardErrorCorrection::CreateUlpfec(kUnknownSsrc)) {}
 
 UlpfecGenerator::UlpfecGenerator(std::unique_ptr<ForwardErrorCorrection> fec)
     : fec_(std::move(fec)),
       num_protected_frames_(0),
       min_num_media_packets_(1) {
   memset(&params_, 0, sizeof(params_));
   memset(&new_params_, 0, sizeof(new_params_));
 }
 
 UlpfecGenerator::~UlpfecGenerator() = default;
@@ skipping 134 matching lines @@
   return (num_fec_packets << 8) / media_packets_.size();
 }
 
 void UlpfecGenerator::ResetState() {
   media_packets_.clear();
   generated_fec_packets_.clear();
   num_protected_frames_ = 0;
 }
 
 }  // namespace webrtc