Streaming media

From Wikipedia, the free encyclopedia

(Redirected from Video streaming)
Jump to: navigation, search
This article relies largely or entirely upon a single source.
Please help improve this article by introducing appropriate citations of additional sources.

Streaming media is multimedia that is constantly received by, and normally displayed to, the end-user while it is being delivered by the provider. 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.

Contents

[edit] 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, due primarily to the high cost and limited capabilities of computer hardware.

Academic experiments in the 1970s proved out the basic concepts and feasibility of streaming media on computers.

During the late 1980s, consumer-grade 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 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. 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 are 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.

[edit] Streaming bandwidth and storage

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) / 8,388.608

(since 1 megabyte = 8 * 1,048,576 bits = 8,388.608 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) / 8,388.608 = 128.7 MiB of storage

If the file is stored on a server for on-demand streaming and this stream is viewed by 1,000 people 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 125.73 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 bandwidth. See below for more information on these protocols.

[edit] Protocol issues

Designing a network protocol to support streaming media raises many issues.

Datagram protocols, such as the User Datagram Protocol (UDP), send the media stream as a series of small packets. 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. 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 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. 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.

Another issue is that firewalls are more likely to block UDP-based protocols than TCP-based protocols. [citation needed]Unicast protocols send a separate copy of the media stream from the server to each client. This is simple, but can lead to massive duplication of data on the network. Multicast protocols undertake to send only one copy of the media stream over any given network connection, i.e. along the path between any two network routers. This is a more efficient use of network capacity, but it is much more complex to implement.[citation needed]

Furthermore, the most prominent of multicast protocols, IP Multicast, must be implemented in all nodes between server and client including network routers. As of 2005, most routers on the Internet however do not support IP Multicast, and many firewalls block it.[citation needed] 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. This prevents the server and its network connections from becoming a bottleneck. However, it raises technical, performance, quality, business, and legal issues.

Newer camcorders stream video to a computer over a FireWire connection. This uses a system of time-based reservations to ensure throughput, and can be received by multiple clients at once.[citation needed]

Widespread deployment of streaming media raises scaling and Quality of Service issues. Testing service deployments is a significant problem. Vendors offer equipment to test streaming services across a number of test domains including Scalability, Quality of Service, Quality of experience, and protocol conformance.[citation needed]

[edit] Social and legal issues

Some streaming broadcasters use streaming systems that interfere with the ability to record streams for later playback, either inadvertently, through poor choice of streaming protocol, or deliberately, because they believe it is to their advantage to do so. Broadcasters may be concerned that copies will result in lost sales or that consumers may skip commercials. Whether users have the ability and the right to record streams has become a significant issue in the application of law to cyberspace.

In principle, there is no way to prevent a user from recording a media stream that has been delivered to their computer. Thus, the efforts of broadcasters to prevent this consist of making it inconvenient, or illegal, or both.

Additionally, using DRM (Digital Rights Management) technologies recording the bits that came through can give some control of the reproductions or plays, so if you have a file created to a streaming capture, you will need a license or key to unblock / decrypt the content.

Broadcasters can make it inconvenient to record a stream, for example, by using unpublished data formats or by encrypting the stream. Of course, data formats can be reverse engineered, and encrypted streams must be decrypted with a key that resides—somewhere—on the consumer's computer, so these measures are security through obscurity, at best.

Efforts to make it illegal to record a stream may rely on copyrights, patents, license agreements, or national legislation that implements the anti-circumvention provisions of the WIPO Copyright Treaty.

[edit] References

[edit] See also

 This list may require cleanup to meet Wikipedia's quality standards.
Please help improve this list. It may be poorly defined, unverified or indiscriminate.

[edit] Streaming media technologies

[edit] Stream and transport protocols

[edit] Media container formats

Main articles: Container format and Audio file format

Containers assemble video and audio tracks in a file or data stream. Common examples are AVI, Ogg, QuickTime, RealMedia, ISO MP4 and the Matroska Media Container. Note that old containers, like AVI, are not well suited for streaming.

[edit] Streaming media content providers

Retrieved from "http://en.wikipedia.org/wiki/Streaming_media"
Personal tools