| Streaming (Work in progress 2007) |
Live streaming is where a live event is broadcast in real time, or as near as, on the internet. At its simplest a home PC with a webcam and a modest broadband connection can produce a webcast. At the other extreme major music or sporting events can be watched by thousands using their browsers.
Images and/or sound are captured with appropriate equipment. Anything from a single digital camcorder to a live TV or radio feed.
The output from this equipment is fed into a computer using appropriate interface hardware.
Encoding software on the Computer turns that input into a format suitable for live streaming. Typically this would be RealProducer for Real Video and Audio format or Windows Media Encoder for Windows Media format.
The encoded output is then transmitted via the computers internet connection to streaming servers. NB: the higher the speed of this internet connection, the higher the quality of the images broadcast.
This single stream is received by the streaming servers and re-broadcast, in real time, to multiple viewers via a website link. |
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| 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). |
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.
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| 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, packets are liable to be lost or corrupted in transit. Depending on the protocol and the extent of the loss, the client may be able to recover the data with error correction techniques, may interpolate over the missing data, or may suffer a dropout. |
| Real-time Streaming Protocol (RTSP) |
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. |
| Firewalls |
| Another issue is that firewalls are more likely to block UDP-based protocols than TCP-based protocols. 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. |
| IP Multicast |
| 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) |
| 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. |
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| 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 on the Internet. |
| As of March 31st 2006, many of the UK's commercial radio stations have been restricting live stream access to users from the United Kingdom only. This came as a response to PPL's announcement that they would only grant radio stations the webcasting rights to stream to the UK, or to face additional costs. As a result, visitors from abroad are no longer be able to access these streams. |
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| British & Irish Live Streaming Links |
| Television |
| ITV.com Watch ITV1, ITV2, ITV3 and ITV4 live on the ITV Media Player, a UK IP address is required to view these channels. |
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| Radio |
| BBC Radio Listen to the BBC's national and local radio stations live. |
| Radiofeeds.co.uk The Internet's most comprehensive and most up-to-date list of UK and Irish radio stations simultaneously webcasting live on the net. This site is updated frequently. |
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| Software |
| Apple - Quicktime Download Apples Quicktime Player. |
| Real Player Download Real Player. |
| Windows Media Player Download Windows Media Player. |