Please answer a question about the following article about YouTube:

Since June 2007, YouTube's videos have been available for viewing on a range of Apple products. This required YouTube's content to be transcoded into Apple's preferred video standard, H.264, a process that took several months. YouTube videos can be viewed on devices including Apple TV, iPod Touch and the iPhone. In July 2010, the mobile version of the site was relaunched based on HTML5, avoiding the need to use Adobe Flash Player and optimized for use with touch screen controls. The mobile version is also available as an app for the Android platform. In September 2012, YouTube launched its first app for the iPhone, following the decision to drop YouTube as one of the preloaded apps in the iPhone 5 and iOS 6 operating system. According to GlobalWebIndex, YouTube was used by 35% of smartphone users between April and June 2013, making it the third most used app.

What is Apple's prefered video standard?
H.264