Streaming media - live sound and vision

The days when streaming media sounded like the wrong end of a call to an underwater phone box and looked like a series of slides from an impressionist cartoon are, thankfully, long gone. Streaming media - audio and video that starts to play back as soon as you click to download it - has greatly improved from the early attempts of pioneers such as RealNetworks.

Nowadays, of course, modems are generally faster, and more people have digital links thanks to ISDN, cable modems and even asymmetric digital subscriber line. Compression technology has also improved greatly, as has processor speed, which means that modern chips can handle more complex decompression routines. Best of all is the fact that you can now add streaming media files to your own website very easily, particularly as many of the streaming tools suppliers offer cut-down free software aimed at consumers.

The three challengers
There are three main companies offering competing streaming media formats - Apple, Microsoft and RealNetworks. Microsoft is a latecomer to the market and it's tempting to write off its contribution if you're committed to providing a website that works on more than just Windows. But that would be unfair because, despite its lack of cross-platform compatibility, there are other advantages to the Redmond giant's system.

RealNetworks is the longest established player in the field and the first name that comes to mind when people consider streaming media. Some ISPs such as Demon Internet provide free Real Audio services for pages hosted on their servers. This makes it easy to get started with streaming media, because you won't have the worry of configuring servers or hosting your own content.

Apple's QuickTime is one of the most flexible systems, with a player that will decode just about any format, streaming or not. For viewers on Windows and Macintosh systems, there's a wealth of content available through fast internet links.

All these formats are steadily becoming fairly standards-based, but that doesn't mean you can use any player to play back any type of streaming file. What it does mean, however, is that they all use Real Time Streaming Protocol (RTSP) to access information over the internet.

Like HTTP, RTSP defines a method for a client to request the transfer of a file, and will work over a number of networks. You'll also hear about Real Time Protocol (RTP), which is a lower-level protocol designed to make it easier to deliver continuous streams of information over the net.

In theory, using RTSP means you can play common formats using any media player you like. In practice, things are more difficult. If you're streaming Mpeg, for example, then most systems can play that. But try using QuickTime video format, or one of RealNetworks' file types, and you'll find that you're restricted to clients that understand those formats. This will cause some problems with web browsers.

For the technically minded, RTP sits on top of the UDP layer of the internet protocol (IP), much like DNS. In other words, delivery of data isn't guaranteed. For really high-quality streaming media, you'll have to wait for IPv6 - the next generation of the IP - which provides real options for specifying quality of service.

In the meantime, the way that systems such as Apple's QuickTime TV network operate is by having a network of servers mirroring content on a high-bandwidth network, such as the one operated by Akamai. By bringing the content as close as possible to the end user, the company hopes to reduce the number of hops in the route and minimise the effect of internet congestion. But for the time being, unless you have a lot of money to spend, you'll have to live with that congestion if you want to serve your own media.

There's one more acronym you're likely to come across when you dip a toe into the waters of streaming media - Smil. This is a mark-up language, or more correctly an XML scheme, for controlling streaming media. You can specify, for example, an area within a browser window in which first one and then another media clip will play.

There are plenty of other neat tricks that SMIL can do, helping to provide a degree of interactivity within the world of streaming media. You can use Smil to control the behaviour of clips with QuickTime and Real players, but for the time being, there's no need to worry about it. You can do streaming media without Smil, it just gives web authors more control so they can do fancier things with streaming content. There's not enough space in this feature to fully cover Smil, but we'll elaborate on it in a later feature.

Getting started
We'll assume you want to do something fairly simple, like adding streaming media to an existing website. You could use it to play a welcome message to people on your website or to allow visitors to see your latest TV advert. You might have sound files that you want people to be able to listen to, or a holiday video you want friends to be able to watch without having to first download the entire file.

When you want to stream media, the first thing you need to do is choose which format you're going to use. There are some formats around that don't use RSTP - but they're strictly minority systems - and many of them will migrate to the standards-based system in time. If you want to be sure of reaching a reasonable audience, the choice is really between Apple, Microsoft and RealNetworks.

With three different formats, you need to pick the most appropriate for both your audience and the server that will be hosting your media clips, which needn't be the same one that hosts your web pages.

So just how do you choose the right format? There are a number of things to consider: quality of the media when it's viewed; amount of space taken up on your server; the ease of creating or converting files; the type of server you have access to; and whom you're expecting to view your files, and on which platform.

Choosing between the formats on the basis of quality is hard to do because they are all capable of producing good results. With a choice of multiple Codecs (Coder-Decoders) in QuickTime, for example, you can tweak file size, bit rate and quality to suit your needs. The same can be done with other formats.

Making an objective assessment of the quality of the three systems isn't easy and, for many people, other considerations may take precedence, particularly if you're financially restricted or the choice of platforms is constrained.

There are commercial tools available as well, including Media Cleaner from Terran, which can convert a wide range of formats and save the results ready for streaming on any of the three servers, but it isn't a cheap program. If you want to create lots of media files, it's a worthwhile investment and gives you control over the results. Alternatively, if you're a business you can contract out the work to specialists, but that won't come cheap.

Choosing a platform
Perhaps the most important consideration will be platform choices. While all three major systems are available for both Windows and Macintosh, there are other considerations. At the time of writing, Microsoft's media player for the Mac was only a beta, so many Mac users will be reluctant to download it. QuickTime and RealPlayer are full releases for both platforms, and the RealPlayer is also available in beta form for Solaris on Sparc and Linux on Intel systems.

If reaching the widest possible audience is important to you, then RealPlayer looks like the sound choice at the moment, with QuickTime running a good second. On the server side, you may be constrained by what your ISP offers - if it has free streaming for a particular format, then you're better off using that if you want to get a feel for it.

On the other hand, if you need many streams, then the choice may simply be one of cost. RealNetworks' charges are based on the number of streams, which usually filter down to the pricing models of ISPs offering the service.

Microsoft's streaming server only runs on Microsoft operating systems so, if you want to use it, you'll need to hunt around for an ISP that has Microsoft servers, or run it on a system in-house.

Apple's QuickTime Streaming Server is part of Mac OS X server. It's also a key technology in the company's open source initiative, so you can download it as Darwin Streaming Server and compile it on your own systems.

There are no costs, and it serves an unlimited number of streams. Add to that the fact that you can find binaries on the internet for Solaris, BSD and Linux on a variety of architectures, and it becomes a very attractive proposition for anyone who wants to start streaming on their own network or using their own hardware.

Streaming media may seem like a black art at first, and it's certainly not the most straightforward web technology available, with competing standards and quality suffering on congested links. However, it can be surprisingly simple to get good results.