try to avoid the start time is not 0

@@ -76,6 +76,9 @@ const char * default_acodec_param = "-acodec copy";
 char vcodec_param[1024];
 char acodec_param[1024];
 
+bool first_time_set = false;
+float start_time = 0.0f;
+
 void addinfo(string t, string name, bool bstart){
 	media_type mtype = name.substr(name.length() - 4, name.length()) == ".aac" ? type_audio : type_video;
 	if (bstart) {
@@ -86,6 +89,13 @@ void addinfo(string t, string name, bool bstart){
 		f.end_time_str = t;
 		f.name = name;
 
+		if (!first_time_set) {
+			first_time_set = true;
+			start_time = f.start_time;
+		}
+
+		f.start_time -= start_time;
+
 		media_files[mtype].push_back(f);
 	}
 	else {
@@ -95,6 +105,7 @@ void addinfo(string t, string name, bool bstart){
 			if (files[i].name == name) {
 				files[i].end_time = atof(t.c_str());
 				files[i].end_time_str = t;
+				files[i].end_time -= start_time;
 				break;
 			}
 		}