Subtitles on by default

Hi,

you could do it with a small jQuery snippet.
If you want to switch on the first subtitle track of a video, use this:

jQuery(document).ready(function($){
	$('.mejs-video.svq .mejs-captions-selector-input:not([value="none"])').eq(0).click();
});

Or, if you want to switch on a specific language, you could use this (change “en” to a language code of your choice):

jQuery(document).ready(function($){
	$('.mejs-video.svq .mejs-captions-selector-input[value$="en"]').click();
});

Put the snippet in a custom javascript file that is loaded by your theme or in a script tag in a post/page.