QUALITY COMPARISON Original video Compressed video (for DSL)

information is thrown away, leaving only the most important parts of the picture and sound. Whether you notice the effects of this compression depends on just how much of the file has been discarded.

WHAT IS STREAMING?
When a video or audio file 'streams', it starts playing as soon as enough of the file has transferred to ensure constant playback -- usually within a few seconds of you clicking on it. A none-streaming file must be transferred completely before it can be played. Many people don't want to wait until an entire video has transferred. They're impatient to view it!

DIAL-UP MODEM CONNECTIONS AND BROADBAND (DSL)
If you access the Internet using a 56k modem on a standard telephone line, you'll find that you can only stream relatively poor-quality video clips. These are heavily-compressed and tend to be blurred whenever there is movement.

A broadband connection (also known as DSL or ADSL) is ten times faster, so the quality of streaming clips is that much better.

In some cases a streaming clip detects what kind of connection you have and adjusts itself accordingly. Other sites, including NNOuk.com, give you the option to choose the most appropriate clip yourself.

REALMEDIA AND WINDOWS MEDIA
Real Networks is the market leader in streaming video for the web and you may already have their player installed as part of the Internet Explorer browser (though not with Windows XP). Although some well-known websites such as those from the BBC and Channel 4 have standardised on the Real format, the Real player has been criticised in the past for being 'buggy', invasive and difficult to uninstall.

Microsoft also has its own Windows Media format which plays in the Windows Media Player that comes as part of Windows or can be downloaded. There is much rivalry between the two companies, with Microsoft currently trying to increase its share of this business.

OTHER VIDEO AND AUDIO FORMATS
The MPEG1 format offers high-compression and reasonable picture quality. MPEG2 improves on that and is used in DVDs and digital broadcasting (Freeview and satellite). MPEG4 arrived fairly recently, it offers the best quality so far, and will be used in mobile phones and broadcasting in the future. The latest versions of Real Media, Windows Media and Apple Quicktime, are all based on MPEG4. There is also the open-source XVid MPEG4 codec.

Usually, the audio part of a video is compressed too. The MP3 format, which is hugely popular for music, is based on MPEG.

Windows AVI isn't actually a format, it is a 'container'. So an AVI file can consist of picture and sound that have been compressed using any of a wide number of different video and audio formats. So, it is quite possible to find an AVI file that has the image compressed with DIVX or XVid (both variations of MPEG4) and sound compressed in MP3 format.

This is why, sometimes, when you try to play an AVI, the player attempts to find a suitable 'codec' on the Internet. A codec is a piece of code that tells the computer how to compress and uncompress the picture or sound.

THE FUTURE
As faster broadband access becomes more common in the UK, we should see an increasing number of British websites offering video. However, it is an expensive option to provide, as video files are large and the site must pay for storage and for every byte of data that is downloaded by a visitor.

To give an example... Someone viewing two-minutes of average-quality video in a three-inch-wide window, costs the site the same as a visitor looking at sixty or seventy fairly-large still images. Video is also costly and time-consuming to produce.

OTHER SITES THAT OFFER VIDEO

British Pathe - the whole of the British Pathe news archive is now available to watch online. News and films going back more than 100 years.

Internet Archive - this American site includes a collection of over 48,000 'ephemeral' (advertising, educational, industrial, and amateur) films. Many of these are free of copyright, so can be used in whole or part in your own video productions! Several hundred feature films have now also been added, all of which are in the public domain in the United States.

BBC News Online - a large selection of topical and archive clips in Real format.

SkyNews - a selection of current and recent reports

Last updated: 3 August 2004

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