YouTube's new API forces third party Windows Phone apps to update31
In addition to MetroTube, another YouTube app for the Windows Phone platform called myTube is also going through an update (to version 18.104.22.168) so that it can use the new YouTube API. With the update, myTube now allows users to read comment reply threads, annotations and subtitles.
There is no official Google provided YouTube app on Windows Phone. The last time a YouTube client was offered for the platform, Google forced it to be shut down because Microsoft blocked the ads that play before some of the videos. Google also is negatively affecting Windows Phone third party YouTube apps with the new YouTube API. The latter no longer allows users to see on a search result, the number of views a video has. Also no longer available are related videos, recommendations and subscriptions.
Third party YouTube sites that haven't updated to support the new API will show users a video like the one embedded below.
source: MetroTube (WindowsPhone), myTube (WindowsPhone) via WMPoweruser