diff --git a/README.md b/README.md
index f2d2d52c9..a791194dd 100755
--- a/README.md
+++ b/README.md
@@ -184,6 +184,7 @@ Please select according to languages:
 
 ### V3 changes
 
+* v3.0, 2018-07-22, Replace hex to string to match MIT license. 3.0.33
 * v3.0, 2018-07-22, Replace base64 to match MIT license. 3.0.32
 * v3.0, 2018-07-22, Replace crc32 IEEE and MPEG by pycrc to match MIT license. 3.0.31
 * v3.0, 2018-07-21, Replace crc32 IEEE by golang to match MIT license. 3.0.30
diff --git a/trunk/src/core/srs_core.hpp b/trunk/src/core/srs_core.hpp
index b62795c9f..8e76a8d70 100644
--- a/trunk/src/core/srs_core.hpp
+++ b/trunk/src/core/srs_core.hpp
@@ -27,7 +27,7 @@
 // current release version
 #define VERSION_MAJOR       3
 #define VERSION_MINOR       0
-#define VERSION_REVISION    32
+#define VERSION_REVISION    33
 
 // generated by configure, only macros.
 #include <srs_auto_headers.hpp>
diff --git a/trunk/src/kernel/srs_kernel_utility.cpp b/trunk/src/kernel/srs_kernel_utility.cpp
index a247bf27d..eba746293 100644
--- a/trunk/src/kernel/srs_kernel_utility.cpp
+++ b/trunk/src/kernel/srs_kernel_utility.cpp
@@ -948,33 +948,44 @@ int av_toupper(int c)
     }
     return c;
 }
-
-int ff_hex_to_data(uint8_t* data, const char* p)
-{
-    int c, len, v;
     
-    len = 0;
-    v = 1;
-    for (;;) {
-        p += strspn(p, SPACE_CHARS);
-        if (*p == '\0')
-            break;
-        c = av_toupper((unsigned char) *p++);
-        if (c >= '0' && c <= '9')
-            c = c - '0';
-        else if (c >= 'A' && c <= 'F')
-            c = c - 'A' + 10;
-        else
-            break;
-        v = (v << 4) | c;
-        if (v & 0x100) {
-            if (data)
-                data[len] = v;
-            len++;
-            v = 1;
-        }
+// fromHexChar converts a hex character into its value and a success flag.
+uint8_t srs_from_hex_char(uint8_t c)
+{
+    if ('0' <= c && c <= '9') {
+        return c - '0';
     }
-    return len;
+    if ('a' <= c && c <= 'f') {
+        return c - 'a' + 10;
+    }
+    if ('A' <= c && c <= 'F') {
+        return c - 'A' + 10;
+    }
+    
+    return -1;
+}
+
+int srs_hex_to_data(uint8_t* data, const char* p, int size)
+{
+    if (size <= 0 || (size%2) == 1) {
+        return -1;
+    }
+    
+    for (int i = 0; i < size / 2; i++) {
+        uint8_t a = srs_from_hex_char(p[i*2]);
+        if (a == (uint8_t)-1) {
+            return -1;
+        }
+        
+        uint8_t b = srs_from_hex_char(p[i*2 + 1]);
+        if (b == (uint8_t)-1) {
+            return -1;
+        }
+        
+        data[i] = (a << 4) | b;
+    }
+    
+    return size / 2;
 }
 
 int srs_chunk_header_c0(int perfer_cid, uint32_t timestamp, int32_t payload_length, int8_t message_type, int32_t stream_id, char* cache, int nb_cache)
diff --git a/trunk/src/kernel/srs_kernel_utility.hpp b/trunk/src/kernel/srs_kernel_utility.hpp
index 34b63eaca..19677d776 100644
--- a/trunk/src/kernel/srs_kernel_utility.hpp
+++ b/trunk/src/kernel/srs_kernel_utility.hpp
@@ -161,7 +161,7 @@ extern srs_error_t srs_av_base64_decode(std::string cipher, std::string& plainte
  * for example, p=config='139056E5A0'
  * output hex to data={0x13, 0x90, 0x56, 0xe5, 0xa0}
  */
-extern int ff_hex_to_data(uint8_t* data, const char* p);
+extern int srs_hex_to_data(uint8_t* data, const char* p, int size);
 
 /**
  * generate the c0 chunk header for msg.
diff --git a/trunk/src/protocol/srs_rtsp_stack.cpp b/trunk/src/protocol/srs_rtsp_stack.cpp
index 55a306c7f..ac0083d82 100644
--- a/trunk/src/protocol/srs_rtsp_stack.cpp
+++ b/trunk/src/protocol/srs_rtsp_stack.cpp
@@ -537,8 +537,12 @@ srs_error_t SrsRtspSdp::parse_fmtp_attribute(string attr)
                 
                 char* tmp_sh = new char[item_value.length()];
                 SrsAutoFreeA(char, tmp_sh);
-                int nb_tmp_sh = ff_hex_to_data((uint8_t*)tmp_sh, item_value.c_str());
-                srs_assert(nb_tmp_sh > 0);
+                
+                int nb_tmp_sh = srs_hex_to_data((uint8_t*)tmp_sh, item_value.c_str(), item_value.length());
+                if (nb_tmp_sh <= 0) {
+                    return srs_error_new(ERROR_RTSP_AUDIO_CONFIG, "audio config");
+                }
+                
                 audio_sh.append(tmp_sh, nb_tmp_sh);
             }
         }
diff --git a/trunk/src/utest/srs_utest_kernel.cpp b/trunk/src/utest/srs_utest_kernel.cpp
index 4b6364e1f..e2e66f794 100644
--- a/trunk/src/utest/srs_utest_kernel.cpp
+++ b/trunk/src/utest/srs_utest_kernel.cpp
@@ -1684,5 +1684,28 @@ VOID TEST(KernelUtility, Base64Decode)
     EXPECT_TRUE(expect == plaintext);
 }
 
+VOID TEST(KernelUtility, StringToHex)
+{
+    if (true) {
+        uint8_t h[16];
+        EXPECT_EQ(-1, srs_hex_to_data(h, NULL, 0));
+        EXPECT_EQ(-1, srs_hex_to_data(h, "0", 1));
+        EXPECT_EQ(-1, srs_hex_to_data(h, "0g", 2));
+    }
+    
+    if (true) {
+        string s = "139056E5A0";
+        uint8_t h[16];
+        
+        int n = srs_hex_to_data(h, s.data(), s.length());
+        EXPECT_EQ(n, 5);
+        EXPECT_EQ(0x13, h[0]);
+        EXPECT_EQ(0x90, h[1]);
+        EXPECT_EQ(0x56, h[2]);
+        EXPECT_EQ(0xe5, h[3]);
+        EXPECT_EQ(0xa0, h[4]);
+    }
+}
+
 #endif