Streaming multimedia is multimedia that is constantly received by, and normally displayed to, the end-user while it is being delivered by the provider (the term "to display" is used in this article in a general sense that includes audio playback. Multimedia is media and content that utilizes a combination of different content forms. The end-user is a p concept in Software engineering, referring to an Abstraction of the group of persons who will ultimately operate a piece of software ) 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. A telecommunications network is a network of Telecommunications links and nodes arranged so that messages may be passed from one part of the network to another over g. radio, television) or inherently non-streaming (e. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic g. books, video cassettes, audio CDs). A Book is a set or collection of written printed illustrated or blank sheets made of Paper, Parchment, or other material usually fastened together Videotape is a means of recording images and sound onto Magnetic tape as opposed to movie film. A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio The verb 'to stream' is also derived from this term, meaning to deliver media in this manner.

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.

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

• having enough CPU power and bus bandwidth to support the required data rates
• creating low-latency interrupt paths in the OS to prevent buffer underrun

However, computer networks were still limited, and media was usually delivered over non-streaming channels, such as CD-ROMs. Low latency allows human-unnoticeable delays between an Input being processed and the corresponding Output providing Real time characteristics An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In Computing, buffer underrun or buffer underflow is a state occurring when a buffer used to communicate between two devices or processes CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable

The late 1990's saw:

• greater network bandwidth, especially in the last mile
• increased access to networks, especially the Internet
• use of standard protocols and formats, such as TCP/IP, HTTP, and HTML
• commercialization of the Internet

These advances in computer networking combined with powerful home computers and modern operating systems made streaming media practical and affordable for ordinary consumers. The last Mile is the final leg of delivering connectivity from a communications provider to a customer The Internet is a global system of interconnected Computer networks The Internet Protocol Suite (commonly TCP/IP) is the set of Communications protocols used for the Internet and other similar networks Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. HTML, an initialism of HyperText Markup Language, is the predominant Markup language for Web pages It provides a means to describe the structure Stand-alone Internet radio devices are offering listeners a "no-computer" option for listening to audio streams. An Internet radio device (IRD or network music player is a hardware device that receives and plays audio from Internet radio stations or optionally a user's PC

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. Multimedia is media and content that utilizes a combination of different content forms.

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. The Journal of Multimedia is a peer-reviewed Scientific journal published monthly by Academy Publisher

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) / 8,388. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on A gigabyte (derived from the SI prefix Giga-) is a unit of Information or Computer A terabyte (derived from the prefix Tera- and commonly abbreviated TB) is a measurement term for data storage capacity. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission 608

(since 1 megabyte = 8 * 1,048,576 bits = 8,388. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on 608 kilobits)

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. A kilobit is a unit of information abbreviated kbit (or kb) The standard definition is 1 kilobit = 103 bit = 1000 Bit. The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI In Computer networking unicast transmission is the sending of information packets to a single destination In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission A gibibyte (a contraction of gi ga bi nary byte) is a unit of Information or Computer storage, abbreviated GiB. Of course, using a Multicast protocol the server sends out only a single stream that is common to all users. Multicast is a network addressing method for the delivery of Information to a group of destinations simultaneously using the most efficient strategy Hence, such a stream would only use 300 kbit/s of serving bandwidth. In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission See below for more information on these protocols.

Protocol issues

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

• Datagram protocols, such as the User Datagram Protocol (UDP), send the media stream as a series of small packets. In Information technology, a packet is a formatted unit of Data carried by a Packet mode Computer network. User Datagram Protocol ( UDP) is one of the core protocols of the Internet Protocol Suite. This is simple and efficient; however, there is no mechanism within the protocol to guarantee delivery. It is up to the receiving application to detect loss or corruption and recover data using error correction techniques. In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in If data is lost, the stream may suffer a dropout.
• The Real-time Streaming Protocol (RTSP), Real-time Transport Protocol (RTP) and the Real-time Transport Control Protocol (RTCP) were specifically designed to stream media over networks. The Real Time Streaming Protocol ( RTSP) developed by the IETF and created in 1998 as RFC 2326 is a protocol for use in Streaming media The Real-time Transport Protocol (or RTP) defines a standardized packet format for delivering audio and video over the Internet Real-time Transport Control Protocol ( RTCP) is a sister protocol of the Real-time Transport Protocol (RTP The latter two are built on top of UDP.
• Reliable protocols, such as the Transmission Control Protocol (TCP), guarantee correct delivery of each bit in the media stream. The Transmission Control Protocol (TCP is one of the core protocols of the Internet Protocol Suite. However, they accomplish this with a system of timeouts and retries, which makes them more complex to implement. It also means that when there is data loss on the network, the media stream stalls while the protocol handlers detect the loss and retransmit the missing data. Clients can minimize the effect of this by buffering data for display.
• 

  Multicasting broadcasts the same copy of the multimedia over the entire network to all clients
  Unicast protocols send a separate copy of the media stream from the server to each client. In Computer networking unicast transmission is the sending of information packets to a single destination In terms of difficulty of implementing technically, these protocols are the most simplistic. At the cost of this simplicity, there can be massive duplication of the data being sent on the network.
• Multicast protocols were developed to try to cut down on the duplication that Unicast protocols cause. Multicast is a network addressing method for the delivery of Information to a group of destinations simultaneously using the most efficient strategy These protocols send only one copy of the media stream over any given network connection, i. e. along the path between any two network routers. Many of these protocols require special routing hardware capable of broadcasting the stream. These multicasts are one-way connections which very closely mirror the functionality of over the air television in that viewers lose their on-demand viewing abilities. Some of these lost viewing abilities include rewinding and fastforwarding a media file. There exist streaming media servers which combine Unicast and Multicast solutions to both cut down on the bandwidth requirements and provide users most of the on-demand functionality of a pure unicast. ^[1]
• IP Multicast, the most prominent of multicast protocols, must be implemented in all nodes between server and client including network routers. IP Multicast is a method of forwarding IP Datagrams to a group of interested receivers As of 2005, most routers on the Internet however do not support IP Multicast, and many firewalls block it. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. IP Multicast is most practical for organizations that run their own networks, such as universities and corporations. Since they buy their own routers and run their own network links, they can decide if the cost and effort of supporting IP Multicast is justified by the resulting bandwidth savings.
• Peer-to-peer (P2P) protocols arrange for media to be sent from clients that already have them to clients that do not. For other uses of the term see Peer-to-peer (disambiguation For peer-to-peer networks used for file sharing see File sharing This prevents the server and its network connections from becoming a bottleneck. However, it raises technical, performance, quality, business, and legal issues.

See also

• List of streaming media systems
• Push technology