Set actual transport overhead in rtp_rtcp

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.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 426 matching lines @@
   }
 
   size_t mtu = rtp_sender_.MaxPayloadLength() + packet_overhead_;
   size_t max_payload_length = mtu - packet_overhead;
   packet_overhead_ = packet_overhead;
   rtcp_sender_.SetMaxPayloadLength(max_payload_length);
   rtp_sender_.SetMaxPayloadLength(max_payload_length);
   return 0;
 }
 
+void ModuleRtpRtcpImpl::SetTransportOverhead(
+    int transport_overhead_per_packet_byte) {
+  if (transport_overhead_per_packet_byte == packet_overhead_) {

[the sun, 2016/10/24 08:35:35]

Is there a valid range for the input, which you can DCHECK?

[the sun, 2016/10/24 08:35:35]

Is this optimization really necessary?

[michaelt, 2016/10/24 09:15:26]

Yes added DCHECKS

[michaelt, 2016/10/24 09:15:26]

We can remove it. SetTransportOverhead should not be called often during a call.
So the better readable code will be more worth than the optimization.  

+    // Ok same as before.
+    return;
+  }
+
+  size_t mtu = rtp_sender_.MaxPayloadLength() + packet_overhead_;
+  size_t max_payload_length = mtu - transport_overhead_per_packet_byte;
+  packet_overhead_ = transport_overhead_per_packet_byte;
+  rtcp_sender_.SetMaxPayloadLength(max_payload_length);
+  rtp_sender_.SetMaxPayloadLength(max_payload_length);
+}
+
 int32_t ModuleRtpRtcpImpl::SetMaxTransferUnit(uint16_t mtu) {
   RTC_DCHECK_LE(mtu, IP_PACKET_SIZE) << "MTU too large: " << mtu;
   RTC_DCHECK_GT(mtu, packet_overhead_) << "MTU too small: " << mtu;
   size_t max_payload_length = mtu - packet_overhead_;
   rtcp_sender_.SetMaxPayloadLength(max_payload_length);
   rtp_sender_.SetMaxPayloadLength(max_payload_length);
   return 0;
 }
 
 RtcpMode ModuleRtpRtcpImpl::RTCP() const {
@@ skipping 476 matching lines @@
 void ModuleRtpRtcpImpl::RegisterSendChannelRtpStatisticsCallback(
     StreamDataCountersCallback* callback) {
   rtp_sender_.RegisterRtpStatisticsCallback(callback);
 }
 
 StreamDataCountersCallback*
     ModuleRtpRtcpImpl::GetSendChannelRtpStatisticsCallback() const {
   return rtp_sender_.GetRtpStatisticsCallback();
 }
 }  // namespace webrtc