Add RTX codecs for codecs only supported by external encoder.

webrtc/media/base/mediaconstants.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 83 matching lines @@
 const char kVp8CodecName[] = "VP8";
 const char kVp9CodecName[] = "VP9";
 const char kH264CodecName[] = "H264";
 
 // RFC 6184 RTP Payload Format for H.264 video
 const char kH264FmtpProfileLevelId[] = "profile-level-id";
 const char kH264FmtpLevelAsymmetryAllowed[] = "level-asymmetry-allowed";
 const char kH264FmtpPacketizationMode[] = "packetization-mode";
 const char kH264ProfileLevelConstrainedBaseline[] = "42e01f";
 
+const int kDynamicPayloadTypeMin = 96;
 const int kDefaultVp8PlType = 100;
 const int kDefaultVp9PlType = 101;
 const int kDefaultH264PlType = 107;
 const int kDefaultRedPlType = 116;
 const int kDefaultUlpfecType = 117;
 const int kDefaultRtxVp8PlType = 96;
 const int kDefaultRtxVp9PlType = 97;
 const int kDefaultRtxRedPlType = 98;
 const int kDefaultRtxH264PlType = 99;
 
 const int kDefaultVideoMaxWidth = 640;
 const int kDefaultVideoMaxHeight = 400;
 const int kDefaultVideoMaxFramerate = 30;
 }  // namespace cricket