I have tried to play a youtube video by its URL by my android program. I have used setVideoURI(uri); function also to set URI, as suggested by other POSTs in stackoverflow
On Android devices, you can use an Intent for Youtube videos:
Intent
Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.youtube.com/watch?v=E43mgXNl0xc")); startActivity(browserIntent);