diff --git a/webrtc/RtpExt.cpp b/webrtc/RtpExt.cpp
index e1e181a6..10542843 100644
--- a/webrtc/RtpExt.cpp
+++ b/webrtc/RtpExt.cpp
@@ -34,6 +34,7 @@ public:
     static constexpr uint16_t kMinSize = 1;
     size_t getSize() const;
     uint8_t getId() const;
+    void setId(uint8_t id);
     uint8_t* getData();
 
 private:
@@ -64,6 +65,7 @@ public:
 
     size_t getSize() const;
     uint8_t getId() const;
+    void setId(uint8_t id);
     uint8_t* getData();
 
 private:
@@ -86,6 +88,10 @@ uint8_t RtpExtOneByte::getId() const {
     return id;
 }
 
+void RtpExtOneByte::setId(uint8_t in) {
+    id = in & 0x0F;
+}
+
 uint8_t *RtpExtOneByte::getData() {
     return data;
 }
@@ -100,6 +106,10 @@ uint8_t RtpExtTwoByte::getId() const {
     return id;
 }
 
+void RtpExtTwoByte::setId(uint8_t in) {
+    id = in;
+}
+
 uint8_t *RtpExtTwoByte::getData() {
     return data;
 }
@@ -118,7 +128,17 @@ static RtpExtType getExtTypeById(uint8_t id, const RtcMedia &media){
 }
 
 template<typename Type>
-static void appendExt( map<RtpExtType, RtpExt> &ret,const RtcMedia &media, uint8_t *ptr, const uint8_t *end){
+static bool isOneByteExt(){
+    return false;
+}
+
+template<>
+static bool isOneByteExt<RtpExtOneByte>(){
+    return true;
+}
+
+template<typename Type>
+static void appendExt(map<RtpExtType, RtpExt> &ret, const RtcMedia &media, uint8_t *ptr, const uint8_t *end) {
     while (ptr < end) {
         auto ext = reinterpret_cast<Type *>(ptr);
         if (ext->getId() == (uint8_t) RtpExtType::padding) {
@@ -131,11 +151,17 @@ static void appendExt( map<RtpExtType, RtpExt> &ret,const RtcMedia &media, uint8
         CHECK(reinterpret_cast<uint8_t *>(ext) + Type::kMinSize <= end);
         CHECK(ext->getData() + ext->getSize() <= end);
         auto type = getExtTypeById(ext->getId(), media);
-        ret.emplace(type, RtpExt(type, ext->getId(), reinterpret_cast<char *>(ext->getData()), ext->getSize()));
+        ret.emplace(type, RtpExt(ext, isOneByteExt<Type>(), type, reinterpret_cast<char *>(ext->getData()), ext->getSize()));
         ptr += Type::kMinSize + ext->getSize();
     }
 }
 
+RtpExt::RtpExt(void *ptr, bool one_byte_ext, RtpExtType type, const char *str, size_t size) : std::string(str, size) {
+    _ptr = ptr;
+    _one_byte_ext = one_byte_ext;
+    _type = type;
+}
+
 map<RtpExtType/*type*/, RtpExt/*data*/> RtpExt::getExtValue(const RtpHeader *header, const RtcMedia &media) {
     map<RtpExtType, RtpExt> ret;
     assert(header);
@@ -274,8 +300,7 @@ string RtpExt::dumpString() const {
             break;
         }
         default: {
-            printer << getExtName(_type) << ", id:" << (int) _id << ", ";
-            printer << "hex:" << hexdump(data(), size());
+            printer << getExtName(_type) << ", hex:" << hexdump(data(), size());
             break;
         }
     }
@@ -498,3 +523,14 @@ uint8_t RtpExt::getFramemarkingTID() const {
     CHECK(_type == RtpExtType::framemarking && size() >= 3);
     return (*this)[0] & 0x07;
 }
+
+void RtpExt::setExtId(uint8_t ext_id) {
+    assert(ext_id > (int) RtpExtType::padding && ext_id <= (int) RtpExtType::reserved && _ptr);
+    if (_one_byte_ext) {
+        auto ptr = reinterpret_cast<RtpExtOneByte *>(_ptr);
+        ptr->setId(ext_id);
+    } else {
+        auto ptr = reinterpret_cast<RtpExtTwoByte *>(_ptr);
+        ptr->setId(ext_id);
+    }
+}
diff --git a/webrtc/RtpExt.h b/webrtc/RtpExt.h
index 0decaeac..2557dc6d 100644
--- a/webrtc/RtpExt.h
+++ b/webrtc/RtpExt.h
@@ -40,14 +40,16 @@ enum class RtpExtType : uint8_t {
     toffset = 14,
     reserved = 15,
     // e2e ?
-    encrypt
+    encrypt = reserved
 };
 
 class RtcMedia;
 
 class RtpExt : public std::string {
 public:
-    RtpExt(RtpExtType type, uint8_t id, const char *str, size_t size) : std::string(str, size), _type(type), _id(id) {}
+    template<typename Type>
+    friend void appendExt(map<RtpExtType, RtpExt> &ret, const RtcMedia &media, uint8_t *ptr, const uint8_t *end);
+
     ~RtpExt() = default;
 
     static map<RtpExtType/*type*/, RtpExt/*data*/> getExtValue(const RtpHeader *header, const RtcMedia &media);
@@ -85,9 +87,16 @@ public:
 
     uint8_t getFramemarkingTID() const;
 
+    //危险函数，必须保证关联的RtpHeader对象有效
+    void setExtId(uint8_t ext_id);
+
 private:
+    RtpExt(void *ptr, bool one_byte_ext, RtpExtType type, const char *str, size_t size);
+
+private:
+    void *_ptr = nullptr;
+    bool _one_byte_ext = true;
     RtpExtType _type;
-    uint8_t _id;
 };