Streaming media

Streaming multimedia is multimedia that is constantly received by, and normally presented to, an end-user while it is being delivered by a streaming provider (the term "presented" is used in this article in a general sense that includes audio or video playback). The name refers to the delivery method of the medium rather than to the medium itself. The distinction is usually applied to media that are distributed over telecommunications networks, as most other delivery systems are either inherently streaming (e.g. radio, television) or inherently non-streaming (e.g. books, video cassettes, audio CDs). The verb 'to stream' is also derived from this term, meaning to deliver media in this manner.

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History

Attempts to display media on computers date back to the earliest days of computing, in the mid-20th century. However, little progress was made for several decades, primarily due to the high cost and limited capabilities of computer hardware.

From the late 1980s through the 1990s, consumer-grade personal computers became powerful enough to display various media. The primary technical issues with streaming were:

However, computer networks were still limited, and media was usually delivered over non-streaming channels, such as CD-ROMs.

The late 1990s and early 2000s, internet users saw:

These advances in computer networking combined with powerful home computers and modern operating systems made streaming media practical and affordable for ordinary consumers. Stand-alone Internet radio devices are offering listeners a "no-computer" option for listening to audio streams.

In general, multimedia content is large, so media storage and transmission costs are still significant; to offset this somewhat, media is generally compressed for both storage and streaming.

A media stream can be on demand or live. On demand streams are stored on a server for a long period of time, and are available to be transmitted at a user's request. Live streams are only available at one particular time, as in a video stream of a live sporting event.

Research in streaming media is ongoing and representative research can be found at the Journal of Multimedia.

Streaming bandwidth and storage

Unicast Connections require multiple connections from the same streaming server even when it streams the same content

Streaming media storage size (in the common file system measurements megabytes, gigabytes, terabytes, and so on) is calculated from streaming bandwidth and length of the media with the following formula (for a single user and file):

storage size (in megabytes) = length (in seconds) * bit rate (in kbit/s) / (8 * 1024)

(since 1 megabyte = 8 * 1,024 kbits)

Real world example:

One hour of video encoded at 300 kbit/s (this is a typical broadband video for 2005 and it's usually encoded in a 320×240 pixels window size) will be:

(3,600 s * 300 kbit/s) / (8*1024) give around 130 MB of storage

If the file is stored on a server for on-demand streaming and this stream is viewed by 1,000 people at the same time using a Unicast protocol, you would need:

300 kbit/s * 1,000 = 300,000 kbit/s = 300 Mbit/s of bandwidth

This is equivalent to around 125 GiB per hour. Of course, using a Multicast protocol the server sends out only a single stream that is common to all users. Hence, such a stream would only use 300 kbit/s of serving bandwidth. See below for more information on these protocols.

Protocol issues

Designing a network protocol to support streaming media raises many issues, such as:

See also