man youtube-dl
OUTPUT TEMPLATE
The -o option allows users to indicate a template for the output file names.
tl;dr: navigate me to examples (#output-template-examples).
The basic usage is not to set any template arguments when downloading a single file,
like in youtube-dl -o funny_video.flv "http://some/video". However, it may contain
special sequences that will be replaced when downloading each video. The special
sequences may be formatted according to python string formatting operations
(https://docs.python.org/2/library/stdtypes.html#string-formatting). For example,
%(NAME)s or %(NAME)05d. To clarify, that is a percent symbol followed by a name in
parentheses, followed by a formatting operations. Allowed names along with sequence
type are:
· id (string): Video identifier
· title (string): Video title
· url (string): Video URL ..................
youtube-dl -o "%(title)s.%(ext)s"