FLV player avoid script data first element not string (#2679 #2680)

兼容不规范的flv流，比如livegbs产生的flv流metadata flv tag解析异常

src/Rtmp/FlvSplitter.cpp

@@ -91,10 +91,12 @@ void FlvSplitter::onRecvContent(const char *data, size_t len) {
         case MSG_DATA3: {
             BufferLikeString buffer(string(data, len));
             AMFDecoder dec(buffer, _type == MSG_DATA3 ? 3 : 0);
-            std::string type = dec.load<std::string>();
+            auto first = dec.load<AMFValue>();
             bool flag = true;
+            if (first.type() == AMFType::AMF_STRING) {
+                auto type = first.as_string();
                 if (type == "@setDataFrame") {
-                std::string type = dec.load<std::string>();
+                    type = dec.load<std::string>();
                     if (type == "onMetaData") {
                         flag = onRecvMetadata(dec.load<AMFValue>());
                     } else {
@@ -105,7 +107,10 @@ void FlvSplitter::onRecvContent(const char *data, size_t len) {
                 } else {
                     WarnL << "unknown notify:" << type;
                 }
-            if(!flag){
+            } else {
+                WarnL << "Parse flv script data failed, invalid amf value: " << first.to_string();
+            }
+            if (!flag) {
                 throw std::invalid_argument("check rtmp metadata failed");
             }
             return;