^start of string
Non-Capturing Group(?:https?://)? ?repeats the group contents below at most once:
httpthe literal text http (case sensitive) s?optionally matches the literal s (11510 / 1638 / 7316) (case sensitive)
Non-Capturing Group(?:www)? ?repeats the group contents below at most once:
wwwthe literal text www (case sensitive) \.the literal . (4610 / 568 / 2E16)
youtubethe literal text youtube (case sensitive) \.the literal . (4610 / 568 / 2E16)
com/watchthe literal text com/watch (case sensitive) \?the literal ? (6310 / 778 / 3F16)
v=the literal text v= (case sensitive) .+?any character (except for line terminators), repeated at least once
?repeats the group contents below at most once:
&the literal & (3810 / 468 / 2616)
.+any character (except for line terminators), repeated at least once
$end of string, or before its final line terminator