Fix Video Loop Issues

[timmyc]

This is still in progress as I still have yet to find a solution for the YouTube looping. This branch seeks to fix #130 - though. While testing out the original report, I noticed that the loop issue was only happening on YouTube embeds, and not on Vimeo embeds. But even when loop was true for Vimeo embeds - they were not looping in the rendered widget.

A fix for the vimeo issue can be seen in dddaa88 ( which apparently has made CI unhappy ). By adding the loop query arg on the Vimeo url, the underlying iframe from Vimeo loops when expected to. YouTube also supports this query arg ( https://developers.google.com/youtube/player_parameters ), but it appears that mediaelement is mangling with the YouTube embed url... because even when the logic in this branch adds the loop query arg appropriately, the iframe src that is subsequently rendered in the widget no longer has the argument:

If I manually add the loop query arg back into the iframe URL seen above, the YouTube video no longer loops.

[timmyc]

Related: mediaelement/mediaelement#1851

and fixed in instructure/mediaelement#17

And released in version 2.23.2 per https://github.com/instructure/mediaelement/blob/master/changelog.md

Version of mejs in trunk is 2.22.0

[obenland]

Maybe we should update the library in 4.8?

[timmyc]

I think it was talked about in the bug scrub today: https://core.trac.wordpress.org/ticket/39686

The issue is to upgrade to a new major version release, so not sure if we can push to do a minor bump to 2.x or not... fwiw any use of wp_video_shortcode with a YouTube video is also affected by this. I need to circle back and see if we can mimic the editor embed flow instead since it isn't looping.

[obenland]

With mediaelement updated, would we still need this proposed change?