You Tube Video Technology

Playback

Viewing YouTube videos on a personal computer requires the Adobe Flash Player plug-in to be installed in the browser. The Adobe Flash Player plug-in is one of the most common pieces of software installed on personal computers and accounts for almost 75% of online video material.

Uploading

Videos uploaded to YouTube by standard account holders are limited to ten minutes in length and a file size of 2 GB. When YouTube was launched in 2005 it was possible to upload longer videos, but a ten minute limit was introduced in March 2006 after YouTube found that the majority of videos exceeding this length were unauthorized uploads of television shows and films. Partner accounts are permitted to upload videos longer than ten minutes, subject to acceptance by YouTube.
YouTube accepts videos uploaded in most container formats, including .AVI, .MKV, .MOV, .MP4, DivX, .FLV, and .OGG. These include video codecs such as MPEG-4, MPEG, and .WMV. It also supports 3GP, allowing videos to be uploaded from legacy mobile phones.

Quality and codecs

YouTube originally offered videos at only one quality level, but now has a range of quality levels as well as a format for viewing on mobile phones. The original format displayed videos at a resolution of 320x240 pixels using the H.263 Sorenson Spark codec, with mono MP3 audio.
Since March 2008, YouTube videos have been available in a range of quality levels, with the higher quality levels offering improved picture definition. In November 2008 720p HD support was added.^[71] At the same time, the YouTube player was changed from a 4:3 aspect ratio to a widescreen 16:9. In November 2009, 1080p HD support was added. YouTube videos currently use the H.264/MPEG-4 AVC codec, with stereo AAC audio.

3D videos

In a video posted on July 21, 2009, YouTube software engineer Peter Bradshaw announced that YouTube users can now upload 3D videos. The videos can be viewed in several different ways, including the common anaglyph (cyan/red lens) method which utilizes glasses worn by the viewer to achieve the 3D effect.

HTML5 video playback

YouTube is currently testing HTML5 technology, which allows videos to be viewed without requiring Adobe Flash Player or any other plug-in to be installed. The YouTube site has a page which allows supported browsers to opt in to the HTML5 trial. Only browsers that support the h.264 video codec can play the videos.