'Metadata takes the form:
title
author
copyright
publisher
isbn'

def _metadata(self, metadata):

    title = _('Unknown')
    author = _('Unknown')
    copyright = ''
    publisher = ''
    isbn = ''
    if metadata:
        if (len(metadata.title) >= 1):
            title = metadata.title[0].value
        if (len(metadata.creator) >= 1):
            from calibre.ebooks.metadata import authors_to_string
            author = authors_to_string([x.value for x in metadata.creator])
        if (len(metadata.rights) >= 1):
            copyright = metadata.rights[0].value
        if (len(metadata.publisher) >= 1):
            publisher = metadata.publisher[0].value
    return ('%s\x00%s\x00%s\x00%s\x00%s\x00' % (title, author, copyright, publisher, isbn))
