MetroTube, a popular Windows Phone YouTube app, has been rendered useless by a recent change in YouTube's backend code. The changes appear to have affected other third-party YouTube apps too, and MetroTube has opted to temporarily hide its app from the Windows Phone Store until a fix is in place. Atta Elayyan, a developer of MetroTube, has confirmed to The Verge that the team has pinpointed a fix and is aiming to make this available soon. As it stands, MetroTube is unusable due to the changes.
Google does not provide an official YouTube API for video streams so third-party apps like MetroTube always run the risk from using unofficial workarounds to provide YouTube content — with changes affecting apps several times a year. Lazy Worm Apps says it has witnessed 400,000 unique downloads of its MetroTube app, so there's clearly a market for a YouTube app on Windows Phone.
Unfortunately, official support for YouTube on Windows Phone is limited to the mobile browsing experience. Microsoft has previously complained that its YouTube app was blocked from accessing YouTube metadata in the same way that Android and iOS can. Although Google has built its own iOS and Android YouTube clients, the company says it has no plans to build out additional Windows apps citing a lack of Windows 8 and Windows Phone users.