You are not using original_filename. original_filename is a field in filer file that shows the name of the file at the upload time. There are 3 different 'name' metadata that is available for all filer files:
* filer_obj.name
* filer_obj.file.name
* filer_obj.original_filename
Maybe you should investigate a bit more before making a decision on which of these fields you should use.