support aac_adtstoasc filter to copy mode.

@@ -330,7 +330,8 @@ int SrsFFMPEG::start()
     }
     
     // the codec params is disabled when copy
-    if (acodec != SRS_RTMP_ENCODER_COPY && acodec != SRS_RTMP_ENCODER_NO_AUDIO) {
+    if (acodec != SRS_RTMP_ENCODER_NO_AUDIO) {
+        if (acodec != SRS_RTMP_ENCODER_COPY) {
             params.push_back("-b:a");
             snprintf(tmp, sizeof(tmp), "%d", abitrate * 1000);
             params.push_back(tmp);
@@ -344,7 +345,6 @@ int SrsFFMPEG::start()
             params.push_back(tmp);
             
             // aparams
-        if (!aparams.empty()) {
             std::vector<std::string>::iterator it;
             for (it = aparams.begin(); it != aparams.end(); ++it) {
                 std::string p = *it;
@@ -352,6 +352,20 @@ int SrsFFMPEG::start()
                     params.push_back(p);
                 }
             }
+        } else {
+            // for audio copy.
+            for (int i = 0; i < (int)aparams.size();) {
+                std::string pn = aparams[i++];
+                
+                // aparams, the adts to asc filter "-bsf:a aac_adtstoasc"
+                if (pn == "-bsf:a" && i < (int)aparams.size()) {
+                    std::string pv = aparams[i++];
+                    if (pv == "aac_adtstoasc") {
+                        params.push_back(pn);
+                        params.push_back(pv);
+                    }
+                }
+            }
         }
     }