I found that I can start a YouTube video in stock YouTube player this way:
Intent i = new Intent(Intent.ACTION_VIEW, Uri.parse(\"vnd.youtube:U79wVTdnMpw\"));
On loadvideo don't put:
loadvideo(https://www.youtube.com/watch?v=gQy4I5y1ldg12)
just put
loadvideo(gQy4I5y1ldg12);