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YouTube is a video-sharing website, created by three former PayPal employees in February 2005, on which users can upload, share and view videos.
The company is based in San Bruno, California, and uses Adobe Flash Video and HTML5 technology to display a wide variety of user-generated video content, including movie clips, TV clips, and music videos, as well as amateur content such as video blogging and short original videos. Most of the content on YouTube has been uploaded by individuals, although media corporations including CBS, BBC, VEVO, Hulu, and other organizations offer some of their material via the site, as part of the YouTube partnership program.

Unregistered users may watch videos, and registered users may upload an unlimited number of videos. Videos that are considered to contain potentially offensive content are available only to registered users 18 years old and older. In November 2006, YouTube, LLC was bought by Google Inc. for US$1.65 billion, and now operates as a subsidiary of Google.

Company history

From left to right: Chad Hurley, Steve Chen, and Jawed Karim

YouTube was founded by Chad Hurley, Steve Chen, and Jawed Karim, who were all early employees of PayPal. Hurley had studied design at Indiana University of Pennsylvania, while Chen and Karim studied computer science together at the University of Illinois at Urbana-Champaign.
According to a story that has often been repeated in the media, Hurley and Chen developed the idea for YouTube during the early months of 2005, after they had experienced difficulty sharing videos that had been shot at a dinner party at Chen's apartment in San Francisco. Karim did not attend the party and denied that it had occurred, while Hurley commented that the idea that YouTube was founded after a dinner party "was probably very strengthened by marketing ideas around creating a story that was very digestible".
YouTube began as a venture-funded technology startup, primarily from a $11.5 million investment by Sequoia Capital between November 2005 and April 2006. YouTube's early headquarters were situated above a pizzeria and Japanese restaurant in San Mateo, California. The domain name www.youtube.com was activated on February 14, 2005, and the website was developed over the subsequent months.
The first YouTube video was entitled Me at the zoo, and shows founder Karim at the San Diego Zoo. The video was uploaded on April 23, 2005, and can still be viewed on the site.
YouTube offered the public a beta test of the site in May 2005, six months before the official launch in November 2005. The site grew rapidly, and in July 2006 the company announced that more than 65,000 new videos were being uploaded every day, and that the site was receiving 100 million video views per day. According to data published by market research company comScore, YouTube is the dominant provider of online video in the United States, with a market share of around 43 percent and more than 14 billion videos viewed in May 2010. YouTube says that over 48 hours of new videos are uploaded to the site every minute, and that around three quarters of the material comes from outside the US. It is estimated that in 2007 YouTube consumed as much bandwidth as the entire Internet in 2000. Alexa ranks YouTube as the third most visited website on the Internet, behind Google and Facebook.
The choice of the name www.youtube.com led to problems for a similarly named website, www.utube.com. The owner of the site, Universal Tube & Rollform Equipment, filed a lawsuit against YouTube in November 2006 after being overloaded on a regular basis by people looking for YouTube. Universal Tube has since changed the name of its website to www.utubeonline.com. In October 2006, Google Inc. announced that it had acquired YouTube for $1.65 billion in Google stock, and the deal was finalized on November 13, 2006. Google does not provide detailed figures for YouTube's running costs, and YouTube's revenues in 2007 were noted as "not material" in a regulatory filing. In June 2008, a Forbes magazine article projected the 2008 revenue at $200 million, noting progress in advertising sales.
In November 2008, YouTube reached an agreement with MGM, Lions Gate Entertainment, and CBS, allowing the companies to post full-length films and television episodes on the site, accompanied by advertisements in a section for US viewers called "Shows". The move was intended to create competition with websites such as Hulu, which features material from NBC, Fox, and Disney. In November 2009, YouTube launched a version of "Shows" available to UK viewers, offering around 4,000 full-length shows from more than 60 partners. In January 2010, YouTube introduced an online film rentals service, which is currently available only to users in the US. The service offers over 6,000 films.

YouTube's current headquarters in San Bruno, California

In March 2010, YouTube began free streaming of certain content, including 60 cricket matches of the Indian Premier League. According to YouTube, this was the first worldwide free online broadcast of a major sporting event.
On March 31, 2010, the YouTube website launched a new design, with the aim of simplifying the interface and increasing the time users spend on the site. Google product manager Shiva Rajaraman commented: "We really felt like we needed to step back and remove the clutter." In May 2010, it was reported that YouTube was serving more than two billion videos a day, which it described as "nearly double the prime-time audience of all three major US television networks combined". In May 2011, YouTube reported in its company blog that the site was receiving more than three billion views per day.
In October 2010, Hurley announced that he would be stepping down as chief executive officer of YouTube to take an advisory role, and that Salar Kamangar would take over as head of the company.
In April 2011, James Zern, a YouTube software engineer, revealed that 30 percent of videos accounted for 99 percent of views on the site.

Features

Video technology

Playback

Viewing YouTube videos on a personal computer requires the Adobe Flash Player plug-in to be installed on 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.

In January 2010, YouTube launched an experimental version of the site that uses the built-in multimedia capabilities of web browsers supporting the HTML5 standard. This allows videos to be viewed without requiring Adobe Flash Player or any other plug-in to be installed. The YouTube site has a page that allows supported browsers to opt in to the HTML5 trial. Only browsers that support HTML5 Video using the H.264 or WebM formats can play the videos, and not all videos on the site are available.

Uploading

Videos uploaded to YouTube by standard account holders are limited to 15 minutes in duration. 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. The 10-minute limit was increased to 15 minutes in July 2010. Partner accounts are permitted to upload longer videos, subject to acceptance by YouTube. File size is limited to 2 GB for uploads from YouTube web page, and to 20 GB if Java-based Advanced Uploader is used. In December 2010, YouTube announced that holders of standard accounts would be allowed to upload videos of unlimited length, provided that they either have a good history of following the site's Community Guidelines and policy on copyright, or verify their account using their mobile phone number. YouTube accepts videos uploaded in most container formats, including .AVI, .MKV, .MOV, .MP4, DivX, .FLV, and .ogg and .ogv. These include video formats such as MPEG-4, MPEG, VOB, and .WMV. It also supports 3GP, allowing videos to be uploaded from mobile phones. Videos with progressive scanning or interlaced scanning can be uploaded, but for the best video quality, YouTube prefers interlaced videos to be deinterlaced prior to uploading. All the video formats on YouTube use progressive scanning.

Quality and codecs

YouTube originally offered videos at only one quality level, displayed at a resolution of 320x240 pixels using the Sorenson Spark codec (a variant of H.263), with mono MP3 audio. In June 2007, YouTube added an option to watch videos in 3GP format on mobile phones. In March 2008, a high quality mode was added, which increased the resolution to 480x360 pixels In November 2008, 720p HD support was added. At the time of the 720p launch, the YouTube player was changed from a 4:3 aspect ratio to a widescreen 16:9. With this new feature, YouTube began a switchover to H.264/MPEG-4 AVC as its default video compression format. In November 2009, 1080p HD support was added. In July 2010, YouTube announced that it had launched a range of videos in 4K format, which allows a resolution of up to 4096x3072 pixels

YouTube videos are available in a range of quality levels. The former names of standard quality (SQ), high quality (HQ) and high definition (HD) have been replaced by numerical values representing the vertical resolution of the video. The default video stream is encoded in H.264/MPEG-4 AVC format, with stereo AAC audio.