how about doing it the way hooktube does it? they don't actually use the video URL for the html5 element, but the google video redirector url that calls upon that video. check out here's how they present some despacito random video...
<video id="player-obj" controls="" src="https://redirector.googlevideo.com/videoplayback?ratebypass=yes&mt=1510077993----SKIPPED----amp;utmg=ytap1,,hd720"><source>Your browser does not support HTML5 video.</video>
the code is for the following video page https://hooktube.com/watch?v=72UO0v5ESUo
youtube to mp3 on the other hand has turned into extremely monetized monster that returns now download.html on half of video download requests... annoying...
the 2 links in this answer are to my personal experiences with both resources. how hooktube is nice and fresh and actually helps avoid censorship and geo restrictions.. check it out, it's pretty cool. and youtubeinmp4 is a popup monster now known as ConvertInMp4...