Streaming is the playback of music, video, or other media over the Internet while it progressively downloads. Unlike downloading a file directly, a copy of the streamed file is not retained on the device once the playback stops. Media can be streamed to computers, mobile devices, and dedicated streaming devices that connect to a TV like an Apple TV or an Amazon Fire Stick.
Most music and video streaming services offer content on demand, which lets users listen or watch something whenever they choose. Some services will stream content live as it is produced, known as "live streaming." Other services allow users to stream their own content from one device to another, across a local network or the Internet.
Streaming services use compression to optimize the size of streaming media to save on their bandwidth usage and ensure that content reaches viewers with minimal buffering. Most even keep multiple copies of a file encoded at different bitrates, delivering the best version for the Internet speed available to the viewer. Common audio codecs include MP3 and AAC, while video often uses H.264, HEVC, or VP9. Video and audio streams are then sent across the Internet using specialized application protocols designed for streaming media, most of which operate over the UDP transport protocol.