YouTube is an online video sharing platform owned by Google, founded on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim, and headquartered in San Bruno, California, United States. It is the second-most visited website in the world, after Google Search. It offers different features based on user verification, such as standard or basic features like uploading videos, creating playlists, and using YouTube Music, with limits based on daily activity (verification via phone number or channel history increases feature availability and daily usage limits); intermediate or additional features like longer videos (over 15 minutes), live streaming, custom thumbnails, and creating podcasts; advanced features like content ID appeals, embedding live streams, applying for monetization, clickable links, adding chapters, and pinning comments on videos or posts. As of October 2024, it includes multitask with the improved miniplayer, build, share, and vote on favorite YouTube playlists, set bedtime with Sleep Timer, and an upgrade on YouTube TV.
Video technology YouTube primarily uses the VP9 and H.264/MPEG-4 AVC video codecs, and the Dynamic Adaptive Streaming over HTTP protocol. By January 2019, YouTube had begun rolling out videos in AV1 format, since then videos which are popular have it. In 2021 it was reported that the company was considering requiring AV1 in streaming hardware in order to decrease bandwidth and increase quality. For stereo, video is usually streamed alongside the Opus or AAC audio codecs. For 5.1 sound, Dolby Digital, Dolby Digital Plus, rarely DTS Express or AAC is used. Additionally, some videos may include Eclipsa audio, which combines Opus with IAMF (Immersive Audio Model and Format). Certain music has HE-AAC, which is exclusively available on YouTube Music. Additionally, some videos may have separate audio streams with Dynamic Range Compression and/or Voice Boost. At launch in 2005, viewing YouTube videos on a personal computer required the Adobe Flash Player plug-in to be installed in the browser. MPEG-4 Part 2 streams contained within 3GP containers were also provided for low bandwidth connections. In January 2010, YouTube launched an experimental version of the site that used the built-in multimedia capabilities of Web browsers supporting HTML video. This allowed videos to be viewed without requiring Adobe Flash Player or any other plug-in to be installed. On January 27, 2015, YouTube announced that HTML video would be the default playback method on supported browsers. HTML video streams use Dynamic Adaptive Streaming over HTTP (MPEG-DASH), an HTTP-based adaptive bit-rate streaming solution optimizes the bitrate and quality for the available network. The platform can serve videos at optionally lower resolution levels starting at 144p for smoother playback in areas and countries with limited Internet speeds, improving compatibility, as well as for the preservation of limited cellular data plans. The resolution can be adjusted automatically based on detected connection speed or set manually. From 2008 to 2017, users could add "annotations" to their videos, such as pop-up text messages and hyperlinks, which allowed for interactive videos. By 2019, all annotations had been removed from videos, breaking some videos that depended on the feature. YouTube introduced standardized widgets intended to replace annotations in a cross-platform manner, including "end screens" (a customizable array of thumbnails for specified videos displayed near the end of the video). In 2018, YouTube became an International Standard Name Identifier (ISNI) registry, and announced its intention to begin creating ISNI identifiers to uniquely identify the musicians whose videos it features. Users can verify their account, normally through a mobile phone, to gain the ability to upload videos up to 12 hours in length, as well as produce live streams. Users who have built sufficient channel history and have a good track record of complying with the site's Community Guidelines will also gain access to these aforementioned features as well. When YouTube was launched in 2005, it was possible to upload longer videos, but a 10-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. Videos can be at most 256 GB in size or 12 hours, whichever is less. As of 2021, automatic closed captions using speech recognition technology when a video is uploaded are available in 13 languages, and can be machine-translated during playback. YouTube also offers manual closed captioning as part of its creator studio. YouTube formerly offered a 'Community Captions' feature, where viewers could write and submit captions for public display upon approval by the video uploader, but this was deprecated in September 2020. YouTube accepts the most common container formats, including MP4, Matroska, FLV, AVI, WebM, 3GP, MPEG-PS, and the QuickTime File Format. Some intermediate video formats (i.e., primarily used for professional video editing, not for final delivery or storage) are also accepted, such as ProRes. YouTube provides recommended encoding settings. Each video is identified by an eleven-character case-sensitive alphanumerical Base64 string in the Uniform Resource Locator (URL) which can contain letters, digits, an underscore (_), and a dash (-). In 2018, YouTube added a feature called Premiere which displays a notification to the user mentioning when the video will be available for the first time, like for a live stream but with a prerecorded video. When the scheduled time arrives, the video is aired as a live broadcast with a two-minute countdown. Optionally, a premiere can be initiated immediately.
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