def _filename(self, ifo, description, extension, segment):
        """
        Construct the standard output filename. Should only be used internally
        of the File class.
        """
        if extension.startswith('.'):
            extension = extension[1:]

        # Follow the frame convention of using integer filenames,
        # but stretching to cover partially covered seconds.
        start = int(segment[0])
        end = int(math.ceil(segment[1]))
        duration = str(end-start)
        start = str(start)

        return "%s-%s-%s-%s.%s" % (ifo, description.upper(), start,
                                   duration, extension)
Construct the standard output filename. Should only be used internally
        of the File class.