"Write TIME as a WebVTT formatted timestamp to PORT."
(match time
((h m s ms)
- (format port "~a:~a:~a.~a" h m s ms))))
+ (format port "~2,'0d:~2,'0d:~2,'0d.~3,'0d" h m s ms))))
(define (write-webvtt subtitle port)
"Write SUBTITLE as a WebVTT formatted subtitle to PORT."