Youtube Features

YOUTUBE FEATURES

Video technology
Playback
Viewing YouTube videos on a personal computer needs the Adobe Flash Player plug-in to be installed on the browser.[51]

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.[52] This allows videos to be viewed without requiring Adobe Flash Player or any other plug-in to be installed.[53][54] The YouTube site has a page that allows supported browsers to opt into 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.[55][56]

On January 27, 2015, YouTube announced that HTML5 will be the default playback method on supported browsers. Supported browsers include Google Chrome, Safari 8, and Internet Explorer 11.[57]

YouTube experimented with Dynamic Adaptive Streaming over HTTP (MPEG-DASH), which is an adaptive bit-rate HTTP-based streaming solution optimizing the bitrate and quality for the available network.[58] Currently they are using Adobe Dynamic Streaming for Flash.[59]

Uploading
All YouTube users can upload videos up to 15 minutes each in duration. Users who have a good track record of complying with the site's Community Guidelines may be offered the ability to upload videos up to 12 hours in length, which requires verifying the account, normally through a mobile phone.[60] When YouTube was launched in 2005, it was possible to upload long 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.[61][62] The 10-minute limit was increased to 15 minutes in July 2010.[63] If an up-to-date browser version is used, videos greater than 20 GB can be uploaded.[64]

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.[65] Videos with progressive scanning or interlaced scanning can be uploaded, but for the best video quality, YouTube suggests interlaced videos be deinterlaced before uploading. All the video formats on YouTube use progressive scanning.[66]

Quality and formats
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),[67][68] with mono MP3 audio.[69] In June 2007, YouTube added an option to watch videos in 3GP format on mobile phones.[70] In March 2008, a high quality mode was added, which increased the resolution to 480x360 pixels.[71]

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.[72] 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.[73][74] YouTube has since lowered the maximum resolution to 3840x2160 pixels, which is twice as many pixels in both directions as 1080p.[75]

In June 2014, YouTube introduced videos playing at 60 frames per second, in order to reproduce video games with a frame rate comparable to high-end graphics cards.[76][77] The videos play back at a resolution of 720p or higher.[78]


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 the VP9 format with stereo Opus audio; if VP9/WebM is not supported in the browser/device or the browser's user agent reports Windows XP, then H.264/MPEG-4 AVC video with stereo AAC audio is used instead.[79]