diff --git a/api/rtpparameters.cc b/api/rtpparameters.cc
index 79fd3a9..cb9c1cf 100644
--- a/api/rtpparameters.cc
+++ b/api/rtpparameters.cc
@@ -114,6 +114,9 @@
     "http://www.webrtc.org/experiments/rtp-hdrext/video-timing";
 const int RtpExtension::kVideoTimingDefaultId = 8;
 
+const char RtpExtension::kMidUri[] = "urn:ietf:params:rtp-hdrext:sdes:mid";
+const int RtpExtension::kMidDefaultId = 9;
+
 const char RtpExtension::kEncryptHeaderExtensionsUri[] =
     "urn:ietf:params:rtp-hdrext:encrypt";
 
@@ -122,7 +125,8 @@
 
 bool RtpExtension::IsSupportedForAudio(const std::string& uri) {
   return uri == webrtc::RtpExtension::kAudioLevelUri ||
-         uri == webrtc::RtpExtension::kTransportSequenceNumberUri;
+         uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
+         uri == webrtc::RtpExtension::kMidUri;
 }
 
 bool RtpExtension::IsSupportedForVideo(const std::string& uri) {
@@ -132,7 +136,8 @@
          uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
          uri == webrtc::RtpExtension::kPlayoutDelayUri ||
          uri == webrtc::RtpExtension::kVideoContentTypeUri ||
-         uri == webrtc::RtpExtension::kVideoTimingUri;
+         uri == webrtc::RtpExtension::kVideoTimingUri ||
+         uri == webrtc::RtpExtension::kMidUri;
 }
 
 bool RtpExtension::IsEncryptionSupported(const std::string& uri) {
@@ -149,7 +154,8 @@
          uri == webrtc::RtpExtension::kVideoRotationUri ||
          uri == webrtc::RtpExtension::kTransportSequenceNumberUri ||
          uri == webrtc::RtpExtension::kPlayoutDelayUri ||
-         uri == webrtc::RtpExtension::kVideoContentTypeUri;
+         uri == webrtc::RtpExtension::kVideoContentTypeUri ||
+         uri == webrtc::RtpExtension::kMidUri;
 }
 
 const RtpExtension* RtpExtension::FindHeaderExtensionByUri(
diff --git a/api/rtpparameters.h b/api/rtpparameters.h
index d9ac1b6..12e0419 100644
--- a/api/rtpparameters.h
+++ b/api/rtpparameters.h
@@ -276,6 +276,11 @@
   static const char kPlayoutDelayUri[];
   static const int kPlayoutDelayDefaultId;
 
+  // Header extension for identifying media section within a transport.
+  // https://tools.ietf.org/html/draft-ietf-mmusic-sdp-bundle-negotiation-49#section-15
+  static const char kMidUri[];
+  static const int kMidDefaultId;
+
   // Encryption of Header Extensions, see RFC 6904 for details:
   // https://tools.ietf.org/html/rfc6904
   static const char kEncryptHeaderExtensionsUri[];