WEBVTT

NOTE vertical spec: https://www.w3.org/TR/webvtt1/#webvtt-alignment-cue-setting

00:00:00.000 --> 00:00:01.234 vertical:rl
Vertical right-to-left (e.g. Japanese)

00:02.345 --> 00:03.456 vertical:lr
Vertical left-to-right (e.g. Mongolian)

00:04.000 --> 00:05.000
No vertical setting (i.e. horizontal)