preference using slashes: "-f 22/17/18".
"-f mp4" and "-f flv" are also supported.
You can also use the special names "best",
- "bestaudio", "worst", and "worstaudio"
+ "bestaudio", "worst", and "worstaudio". By
+ default, youtube-dl will pick the best
+ quality.
--all-formats download all available video formats
--prefer-free-formats prefer free video formats unless a specific
one is requested