Allow a received audio codec's payload type to change.

webrtc/api/audio_codecs/audio_format.h

 /*
  *  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 23 matching lines @@
   SdpAudioFormat(const char* name,
                  int clockrate_hz,
                  size_t num_channels,
                  const Parameters& param);
   SdpAudioFormat(const std::string& name,
                  int clockrate_hz,
                  size_t num_channels,
                  const Parameters& param);
   ~SdpAudioFormat();
 
+  // Returns true if this format is compatible with |o|. In SDP terminology:
+  // would it represent the same codec between an offer and an answer? As
+  // opposed to operator==, this method disregards codec parameters.
+  bool Matches(const SdpAudioFormat& o) const;
+
   SdpAudioFormat& operator=(const SdpAudioFormat&);
   SdpAudioFormat& operator=(SdpAudioFormat&&);
 
   friend bool operator==(const SdpAudioFormat& a, const SdpAudioFormat& b);
   friend bool operator!=(const SdpAudioFormat& a, const SdpAudioFormat& b) {
     return !(a == b);
   }
 
   std::string name;
   int clockrate_hz;
@@ skipping 70 matching lines @@
 
   bool operator!=(const AudioCodecSpec& b) const { return !(*this == b); }
 
   SdpAudioFormat format;
   AudioCodecInfo info;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_AUDIO_CODECS_AUDIO_FORMAT_H_