Content accessibility
On YouTube
YouTube accepts common video file formats and converts them to Flash Video in order to make them available for online viewing. Since June 2007, newly uploaded videos have also been encoded using the H.264 video standard to enable streaming of YouTube videos on the Apple TV, iPhone, and iPod touch.
On Apple TV
Apple Inc. announced on 20 June 2007 that YouTube is accessible on the Apple TV after installation of a free software update. Functionality includes browsing by category, searching videos, and the ability for members to log onto their YouTube accounts directly on Apple TV. Access to thousands of the most current and popular YouTube videos are available, and there were plans to add thousands more videos each week. The entire catalog was targeted to be available in fall 2007. According to Apple VP David Moody, the reason for the delay was the need for all current YouTube content to be transcoded to Apple's preferred video standard, H.264.
On mobile
YouTube launched its mobile site, YouTube Mobile on 15 June 2007. It is based on xHTML and uses 3GP videos with H.263/AMR codec and RTSP streaming. It is available via a web interface at m.youtube.com or via YouTube's Mobile Java Application.
On TV
YouTube TV Channel is on Information TV 2, and it started January 7, 2008. The channel is airing video sharing content from the YouTube website.
On iPhone and iPod touch
Apple announced Wednesday, 20 June 2007 that YouTube would be available on iPhone at launch. Streaming is over Wi-Fi or EDGE.
Videos on YouTube for the iPhone are encoded in Apple's preferred H.264 format. All videos are viewed in the horizontal orientation of the phone. As YouTube videos have 4:3 aspect ratio and the iPhone is 3:2, videos must be viewed with black bars on the side (pillarboxed) or may be zoomed to trim some of the top and bottom to fill the screen.
Not all videos were available on iPhone initially because not every video was reencoded to H.264. There are two versions of each video on YouTube, one is higher bandwidth for Wi-Fi use, and one is lower resolution for EDGE use.
Unlike the Apple TV version, users cannot log in to their own YouTube accounts, but can create a separate favorites list just for the iPhone.
Outside YouTube
Each YouTube video is accompanied by a piece of HTML markup which can be used to link to the video or embed it on a page outside the YouTube website, unless the submitter of a video chooses to disable the feature. A small addition to the markup allows the video to play automatically when the webpage loads. These options are especially popular with users of social networking sites. YouTube videos can also be accessed via a gadget which is available for the iGoogle homepage.[45]
YouTube videos are designed to be viewed while connected to the internet, and no official feature allows for them to be downloaded and viewed offline.[46] However, a number of third-party web sites, applications and browser extensions (such as Firefox extensions) exist for this purpose.[47]. Alternatively, .flv files can be copied from the 'Temporary Internet Files' folder in Windows, or the /tmp directory in GNU systems, to a permanent folder. The .flv files can then be viewed and edited directly or converted to other formats using various applications such as VLC media player.
source:Wikipedia
