fix warning

@@ -24,7 +24,7 @@ enum media_type{
 };
 vector<fileinfo>  media_files[2];
 
-void run_shell_cmd(char * cmd)
+void run_shell_cmd(const char * cmd)
 {
 	if (only_print){
 		printf("\n%s", cmd);
@@ -34,8 +34,9 @@ void run_shell_cmd(char * cmd)
 	}
 }
 
-char * default_vcodec_param = " -vcodec libx264 -level 3.1 -preset veryfast -g 40 -r 20 ";
-char * default_acodec_param = " -acodec copy ";
+const char * default_vcodec_param = " -vcodec libx264 -level 3.1 -preset veryfast -g 40 -r 20 ";
+const char * default_acodec_param = " -acodec copy ";
+
 char vcodec_param[1024];
 char acodec_param[1024];
 
@@ -224,7 +225,7 @@ int main(int argc, char * argv[])
 	if (argc < 2) {
 		printf("   run ffmpeg to merge audio and video files according to the record info file,\nusage:");
 		printf("\n   %s record_info_filename [-p]", argv[0]);
-		printf("\n   -p :only print the command,don't run ffmpeg");
+		printf("\n   -p :only print the command,don't run ffmpeg\n");
 		return -1;
 	}