Set actual transport overhead in rtp_rtcp

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index c219cb1e001bb793e0461399e774dfcbc9aeade1..5348ff6586f186802d4d0f5df763b62fb13f0a7a 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -444,6 +444,20 @@ int32_t ModuleRtpRtcpImpl::SetTransportOverhead(
   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;