In Xenforo 1.15, when you click to play a YouTube video when using Chrome on a Nexus 7 Android tablet, the video plays back on the page. Here's an example on my website:
Defiance YouTube video
However, in Xenforo 1.2, when clicking on a video it doesn't play it on the page, it instead opens it in the YouTube app.
Here's the same video you can try:
I don't know if this is intentional or not?
Personally I don't like it opening in the YouTube app - it's a second application that isn't needed. I am happy to play it directly on the page and can click on the full screen button if I need to.
The YouTube site itself let's you choose when you click on a video to play it either in Chrome on the Nexus 7 or in the YouTube app. If this could be an option then that would be ideal but if not, the video on the page is IMO more preferable.