Thanks for the plugin!
I had to make a couple of small tweaks to get it to work for me:
- I'd linked my youtube videos using the youtu.be domain, so I had to add "youtu.be" to the $accepted_providers array.
- I'm using the roots framework as the basis for my custom theme and I think that puts the video's iframe in a div with a class of "entry-asset-content". This div couldn't be nested inside the paragraph element used by the responsive video plugin, so I had to change p.rve-embed-container into a div.