How YouTube Streaming Works

By Sue Smith

YouTube provides video streams to computers and smartphones.
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When you watch a video on the YouTube site or a YouTube app on a mobile device, you use media streaming technology. With streaming, you can begin to view playback of a video file without having to first download the complete file to your computer, as you often have to do with other media items such as images. YouTube streaming lets you view various types of video files, sometimes at multiple different resolutions. With a YouTube account, you can upload your own videos for streaming over the service.

Video Formats

YouTube supports a variety of video formats, including FLV (Flash video), MOV (QuickTime), MPEG, AVI, WMV and 3GPP. When you sign up for a YouTube account, you can upload videos with these file types. Internet users can then stream and view your videos via YouTube. YouTube hosts the video files on its servers, sending the video streams to users who browse to the page with your video on it. A user can start viewing your video almost as soon as he browses to the page, depending on the speed of his Internet connection.


The key aspect of streaming is that users can view your media files as they download. When a user browses to a YouTube video, his browser or app software will begin to download the video file. As soon as the computer receives enough of the video stream, the software will begin playback, displaying the video while the rest of it is being downloaded. The control section beneath each video indicates how much of the video has already downloaded, as well as the playback position, along a horizontal bar. Your system will usually store a buffer of downloaded data so that playback is not interrupted if there is a break in the download.


Digital video files contain substantial amounts of data. This means that they tend to be streamed in a compressed form so that downloading the data uses as little bandwidth as possible. Your computer software therefore has to decode the streamed data before you can view it during playback. If you view YouTube videos in a Web browser, for example Internet Explorer or Firefox, this decoding process is typically handled by media player plugins running within the browser application. The software therefore has to handle downloading, decoding and playback functions simultaneously whenever you view a streamed video.

Live Streaming

Live streaming is a developing area for YouTube. Rather than hosting a video file and serving it to users via progressive download as with most YouTube videos, YouTube is able to serve live video virtually in real-time. The YouTube service therefore also has to handle uploading this video content, serving it via streams almost immediately. The ability to serve live streams is naturally dependent on increasing levels of bandwidth for both uploading and downloading at the user end.