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

webrtc/modules/rtp_rtcp/source/flexfec_sender.cc

 /*
  *  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 62 matching lines @@
       payload_type_(payload_type),
       // Reset RTP state if this is not the first time we are operating.
       // Otherwise, randomize the initial timestamp offset and RTP sequence
       // numbers. (This is not intended to be cryptographically strong.)
       timestamp_offset_(rtp_state ? rtp_state->start_timestamp
                                   : random_.Rand<uint32_t>()),
       ssrc_(ssrc),
       protected_media_ssrc_(protected_media_ssrc),
       seq_num_(rtp_state ? rtp_state->sequence_number
                          : random_.Rand(1, kMaxInitRtpSeqNumber)),
-      ulpfec_generator_(ForwardErrorCorrection::CreateFlexfec()),
+      ulpfec_generator_(
+          ForwardErrorCorrection::CreateFlexfec(ssrc, protected_media_ssrc)),
       rtp_header_extension_map_(RegisterBweExtensions(rtp_header_extensions)),
       header_extensions_size_(
           rtp_header_extension_map_.GetTotalLengthInBytes(extension_sizes)) {
   // This object should not have been instantiated if FlexFEC is disabled.
   RTC_DCHECK_GE(payload_type, 0);
   RTC_DCHECK_LE(payload_type, 127);
 }
 
 FlexfecSender::~FlexfecSender() = default;
 
@@ skipping 65 matching lines @@
 }
 
 RtpState FlexfecSender::GetRtpState() {
   RtpState rtp_state;
   rtp_state.sequence_number = seq_num_;
   rtp_state.start_timestamp = timestamp_offset_;
   return rtp_state;
 }
 
 }  // namespace webrtc