format, irrespective of the file format.
-1 for default (order by other properties),
-2 or smaller for less than default.
+ * http_referer HTTP Referer header value to set.
+ * http_method HTTP method to use for the download.
+ * http_headers A dictionary of additional HTTP headers
+ to add to the request.
+ * http_post_data Additional data to send with a POST
+ request.
url: Final video URL.
ext: Video filename extension.
format: The video format, defaults to ext (used for --get-format)