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6. YouTube’s Video Technology

YouTube’s Video Compression

By default, YouTube streams video in the VP9 format with stereo Opus audio. If the user’s device does not support this, then H.264 (MPEG-4 AVC) video is used with stereo AAC audio.

How Does YouTube Deliver Video?

YouTube delivers video over HTTP through a technology called adaptive bitrate streaming. Basically, the video begins playing at a low bitrate. If the client senses that it can handle a higher bitrate, the client asks the server to send a faster bitrate. This process continues until the client and the server decide upon the bitrate most appropriate for streaming the video to that particular user. Thus, the user obtains the highest quality video onscreen that the Internet is able to deliver at that point in time depending on the user’s equipment and the state of traffic (i.e., availability of bandwidth) on the Internet at the time.

How Long Can Your Video Be?

By default, every YouTube user can upload videos up to 15 minutes long. To upload longer videos, you must apply to increase your limit, in which case the maximum file size is 128 GB. Follow this link to learn more about increasing your limit.

What Formats Are Accepted?

YouTube accepts the following video file formats: .MOV, .MPEG4, .MP4, .AVI, .WMV, .MPEGPS, .FLV, .3GPP, and .WebM. Before uploading, interlaced videos should be deinterlaced because YouTube displays video using progressive scanning in which the frames are drawn from top to bottom instead of interlacing the frame by displaying the the odd followed by the even scan lines. Back in the day, interlacing was used in analog television to reduce flicker on the screen.

What Resolutions Are Accepted?

YouTube has gradually increased the frame size limit, which was 320x240 pixels when YouTube started in 2005. In March of 2008, the limit increased to 480x360, and later that year, 720p (1280x720 pixels) began to be supported in November of 2008. 1080p support (1920x1080) came in November 2009, followed by 4K support (3840x2160) in July 2010. In June 2015, YouTube added support for 8K resolution which plays videos at 7680x4320 pixels.

What Frame Rates Are Accepted?

According to the video encoding page at YouTube’s help center, “Content should be encoded and uploaded in the same frame rate it was recorded. Common frame rates include: 24, 25, 30, 48, 50, 60 frames per second (other frame rates are also acceptable). Interlaced content should be deinterlaced before uploading. For example, 1080i60 content should be deinterlaced to 1080p30, going from 60 interlaced fields per second to 30 progressive frames per second.”

360 Degree Videos

YouTube supports 360 degree videos that you can view with Google Cardboard. To learn how to do so, follow this link to 360 degree videos in Cardboard instructions.

Virtual Reality Videos

Virtual reality (VR) videos create a sense of depth by making near things look near, and far things look far. YouTube supports VR videos with Google Cardboard but you can still watch the videos if you do not have a Cardboard viewer, in which case the video will appear as a 360 degree video without 3D. To learn how to create and upload virtual reality videos, follow this YouTube help center link to virtual reality videos.