Streaming media

Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a provider. The verb "to stream" refers to the process of delivering media in this manner; the term refers to the delivery method of the medium rather than the medium itself.

A client media player can begin playing the data (such as a movie) before the entire file has been transmitted. Distinguishing delivery method from the media distributed applies specifically to telecommunications networks, as most of the delivery systems are either inherently streaming (e.g., radio, television) or inherently nonstreaming (e.g., books, video cassettes, audio CDs). For example, in the 1930s, elevator music was among the earliest popularly available streaming media; nowadays Internet television is a common form of streamed media. The term "streaming media" can apply to media other than video and audio such as live closed captioning, ticker tape, and real-time text, which are all considered "streaming text". The term "streaming" was first used in the early 1990s as a better description for video on demand on IP networks; at the time such video was usually referred to as "store and forward video",^[1] which was misleading nomenclature.

Live streaming, which refers to content delivered live over the Internet, requires a form of source media (e.g. a video camera, an audio interface, screen capture software), an encoder to digitize the content, a media publisher, and a content delivery network to distribute and deliver the content

Consumerization of streaming

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 emerged to offer listeners a no-computer option for listening to audio streams. These audio streaming services have become increasingly popular over recent years, as streaming music hit a record of 118.1 billion streams in 2013.^[7] In general, multimedia content has a large volume, so media storage and transmission costs are still significant. To offset this somewhat, media are generally compressed for both storage and streaming.

Increasing consumer demand for streaming of high definition (HD) content has led the industry to develop a number of technologies such as WirelessHD  or ITU-T G.hn, which are optimized for streaming HD content without forcing the user to install new networking cables. In 1996, digital pioneer Marc Scarpa produced the first large-scale, online, live broadcast in history, the Adam Yauch-led Tibetan Freedom Concert, an event that would define the format of social change broadcasts. Scarpa continued to pioneer in the streaming media world with projects such as Woodstock '99, Townhall with President Clinton, and more recently Covered CA's campaign Tell A Friend Get Covered which was live streamed on YouTube.

Today, a media stream can be streamed either live or on demand. Live streams are generally provided by a means called "true streaming". True streaming sends the information straight to the computer or device without saving the file to a hard disk. On-demand streaming is provided by a means called progressive streaming or progressive download. Progressive streaming saves the file to a hard disk and then is played from that location. On-demand streams are often saved to hard disks and servers for extended amounts of time; while the live streams are only available at one time only (e.g., during the football game).^[8]

Streaming media is increasingly being coupled with use of social media. For example, sites such as YouTube encourage social interaction in webcasts through features such aslive chat, online surveys, etc. Furthermore, streaming media is increasingly being used for social business and e-learning

Bandwidth and storage

A broadband speed of 2.5 Mbit/s or more is recommended for streaming movies, for example to a Roku, Apple TV, Google TV or a Sony TV Blu-ray Disc Player, 10 Mbit/s for High Definition content.

storage size (in megabytes) = length (in seconds) × bit rate (in bit/s) / (8 × 1024 × 1024)Streaming media storage size is calculated from the streaming bandwidth and length of the media using the following formula (for a single user and file):

Real world example:

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

(3,600 s × 300,000 bit/s) / (8×1024×1024) requires around 128 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 Unicastprotocol, the requirement is:

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

This is equivalent to around 135 GB per hour. Using a multicast protocol the server sends out only a single stream that is common to all users. Therefore such a stream would only use 300 kbit/s of serving bandwidth. See below for more information on these protocols.

The calculation for live streaming is similar.

Assumptions: speed at the encoder, is 500 kbit/s.

If the show lasts for 3 hours with 3,000 viewers, then the calculation is:

Number of MBs transferred = encoder speed (in bit/s) × number of seconds × number of viewers / (8*1024*1024)

Number of MBs transferred = 500 x 1024 (bit/s) × 3 × 3,600 ( = 3 hours) × 3,000 (number of viewers) / (8*1024*1024) = 1,977,539 MB

Protocols

The audio stream is compressed using an audio codec such as MP3, Vorbis or AAC.

The video stream is compressed using a video codec such as H.264 or VP8.

Encoded audio and video streams are assembled in a container bitstream such as MP4, FLV, WebM, ASF or ISMA.

The bitstream is delivered from a streaming server to a streaming client using a transport protocol, such as MMS or RTP. Newer technologies such as HLS, Microsoft's Smooth Streaming, Adobe's HDS and finally MPEG-DASH have emerged to enable adaptive bitrate streaming over HTTP as an alternative to using proprietary transport protocols.

The streaming client may interact with the streaming server using a control protocol, such as MMS or RTSP.

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