diff --git a/trunk/src/app/srs_app_rtc_sdp.cpp b/trunk/src/app/srs_app_rtc_sdp.cpp
index a26195044..4c3d9f53c 100644
--- a/trunk/src/app/srs_app_rtc_sdp.cpp
+++ b/trunk/src/app/srs_app_rtc_sdp.cpp
@@ -330,6 +330,9 @@ srs_error_t SrsMediaDesc::encode(std::ostringstream& os)
         os << kCRLF;
     }
 
+    for(map<int, string>::iterator it = extmaps_.begin(); it != extmaps_.end(); ++it) {
+        os << "a=extmap:"<< it->first<< " "<< it->second<< kCRLF;
+    }
     if (sendonly_) {
         os << "a=sendonly" << kCRLF;
     }
@@ -399,8 +402,7 @@ srs_error_t SrsMediaDesc::parse_attribute(const std::string& content)
     }
 
     if (attribute == "extmap") {
-        // TODO:We don't parse "extmap" currently.
-        return 0;
+        return parse_attr_extmap(value);
     } else if (attribute == "rtpmap") {
         return parse_attr_rtpmap(value);
     } else if (attribute == "rtcp") {
@@ -435,6 +437,20 @@ srs_error_t SrsMediaDesc::parse_attribute(const std::string& content)
 
     return err;
 }
+srs_error_t SrsMediaDesc::parse_attr_extmap(const std::string& value)
+{
+    srs_error_t err = srs_success;
+    std::istringstream is(value);
+    int id = 0;
+    FETCH(is, id);
+    if(extmaps_.end() != extmaps_.find(id)) {
+        return srs_error_new(ERROR_RTC_SDP_DECODE, "duplicate ext id: %d", id);
+    }
+    string ext;
+    FETCH(is, ext);
+    extmaps_[id] = ext;
+    return err;
+}
 
 srs_error_t SrsMediaDesc::parse_attr_rtpmap(const std::string& value)
 {
diff --git a/trunk/src/app/srs_app_rtc_sdp.hpp b/trunk/src/app/srs_app_rtc_sdp.hpp
index d69293822..b50509f5d 100644
--- a/trunk/src/app/srs_app_rtc_sdp.hpp
+++ b/trunk/src/app/srs_app_rtc_sdp.hpp
@@ -31,6 +31,8 @@
 
 #include <string>
 #include <vector>
+#include <map>
+const std::string kTWCCExt = "http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01";
 
 class SrsSessionInfo
 {
@@ -115,6 +117,7 @@ public:
     srs_error_t encode(std::ostringstream& os);
     SrsMediaPayloadType* find_media_with_payload_type(int payload_type);
     std::vector<SrsMediaPayloadType> find_media_with_encoding_name(const std::string& encoding_name) const;
+    const std::map<int, std::string>& get_extmaps() const { return extmaps_; }
 
     bool is_audio() const { return type_ == "audio"; }
     bool is_video() const { return type_ == "video"; }
@@ -128,6 +131,7 @@ private:
     srs_error_t parse_attr_msid(const std::string& value);
     srs_error_t parse_attr_ssrc(const std::string& value);
     srs_error_t parse_attr_ssrc_group(const std::string& value);
+    srs_error_t parse_attr_extmap(const std::string& value);
 private:
     SrsSSRCInfo& fetch_or_create_ssrc_info(uint32_t ssrc);
 
@@ -153,6 +157,7 @@ public:
     std::vector<SrsCandidate> candidates_;
     std::vector<SrsSSRCGroup> ssrc_groups_;
     std::vector<SrsSSRCInfo>  ssrc_infos_;
+    std::map<int, std::string> extmaps_;
 };
 
 class SrsSdp