Perform command and return the appropriate exit code.

        :rtype: int

def perform_command(self):
        """
        Perform command and return the appropriate exit code.

        :rtype: int
        """
        if len(self.actual_arguments) < 2:
            return self.print_help()
        source_url = self.actual_arguments[0]
        output_file_path = self.actual_arguments[1]

        download = not self.has_option("--list")
        # largest_audio = True by default or if explicitly given
        if self.has_option("--largest-audio"):
            largest_audio = True
        else:
            largest_audio = not self.has_option("--smallest-audio")
        download_format = self.has_option_with_value("--format")

        try:
            if download:
                self.print_info(u"Downloading audio stream from '%s' ..." % source_url)
                downloader = Downloader(logger=self.logger)
                result = downloader.audio_from_youtube(
                    source_url,
                    download=True,
                    output_file_path=output_file_path,
                    download_format=download_format,
                    largest_audio=largest_audio,
                )
                self.print_info(u"Downloading audio stream from '%s' ... done" % source_url)
                self.print_success(u"Downloaded file '%s'" % result)
            else:
                self.print_info(u"Downloading stream info from '%s' ..." % source_url)
                downloader = Downloader(logger=self.logger)
                result = downloader.audio_from_youtube(
                    source_url,
                    download=False
                )
                self.print_info(u"Downloading stream info from '%s' ... done" % source_url)
                msg = []
                msg.append(u"%s\t%s\t%s\t%s" % ("Format", "Extension", "Bitrate", "Size"))
                for r in result:
                    filesize = gf.human_readable_number(r["filesize"])
                    msg.append(u"%s\t%s\t%s\t%s" % (r["format"], r["ext"], r["abr"], filesize))
                self.print_generic(u"Available audio streams:")
                self.print_generic(u"\n".join(msg))
            return self.NO_ERROR_EXIT_CODE
        except ImportError:
            self.print_no_dependency_error()
        except Exception as exc:
            self.print_error(u"An unexpected error occurred while downloading audio from YouTube:")
            self.print_error(u"%s" % exc)

        return self.ERROR_EXIT_CODE