Windows Phone 7 doesn’t have native support for YouTube but it has a YouTube app that integrates pretty well with the system. The fact is – the YouTube integration is present in the system, but it’s hidden.
Whenever you open a YouTube video in Internet Explorer Mobile (on Windows Phone 7 – be it on an actual device or an emulator instance), there is a Watch Video link.
The interesting part is here – it’s not a direct video link but rather an application launcher that has this format:
From what I looked at, I do think it is a functionality directly tied to the system since a specific app is referenced here and if it’s not found locally, the user will be prompted with a download:
In order to be able to access the video, a HTML page should be created with the appropriate link (as a href).
<a href="vnd.youtube:15QoetWd-28?vndapp=youtube_mobile&vndclient=mv-google&vndel=watch">Play Video</a>
I must mention that you cannot simply type this in the IE address bar because direct application calls are not permitted.
Also, if the phone is connected to Zune, the video will not play – make sure the media link is free.