RealAudio

RealAudio - Using audio with SMIL

RealAudio is one of the oldest multimedia techniques on the web. It's been around since the dark ages in 1995 when RealNetworks was still Progressive Networks. This classic technique is now in its sixth generation with the release of the G2 system from Real. RealAudio is an important part of Real's lineup and has been integrated into SMIL.

When combined with SMIL it can work with RealPix, RealText and RealVideo to create compelling multimedia presentations. Its best use is as a backing sound track for a slide show. Adding text and audio to a RealPix slide show can provide a wealth of information in relatively low bandwidth. The RealAudio can also can programmed to respond to the native language of the users machine. When the language is detected alternative RealAudio files can be played to match the RealPix images. This makes for easy to program multi-lingual presentations.

Getting audio to play over a dial up connection can be like trying to suck a bowling ball through a garden hose. Audio delivery has been improving on two fronts over the years. Increased bandwidth allows for better quality through larger file sizes. At the same time Real has gotten better at compressing the audio down to smaller file sizes. The result is that AM radio quality sound can now be heard at approximately 1K/sec or about 14.4 modem bandwidth. Real has been very smart about compression and has once again attacked it on two fronts. Data compression techniques have improved as computers have gotten better at decoding compression. A faster computer can decode better compression in real time to allow better quality delivery. Real has also studied the way people hear sounds. Psycho-acoustical research has taught them that certain frequencies of sound are not heard by humans or can be eliminated without greatly effecting understanding. Eliminating these "useless" frequencies can reduce the file size of the audio file being downloaded. Thus Real has different methods for encoding voice, mixed voice and music and music only. Each of these techniques allows for frequencies important to understanding to be preserved while the rest are highly compressed or eliminated.

Real has not been alone in the market over the years. In the early days, Progressive Networks was just one of the many companies competing for a share of the market. In a similar way to the browser wars the other vendors were weeded out and Real now owns approximately 85% if the streaming audio/video market. Quicktime has always been the main competitor though Apple has only recently made streaming Quicktime an easy-to-use reality. Macromedia has also made use of the wide distribution of their Shockwave plug-in to introduce streaming audio. The benefit of these solutions over Real is that both provide streaming without needing a server. However, Real has recently also introduced streaming without servers to counteract this threat. RealAudio and Video can now be encoded so that they can be streamed from a normal web server without the need of a Real Server. However, Real has added enough enhancements to their Real Server that it remains a great platform. The main competition may come from Microsoft who has introduced their ASF (Active Streaming Format) that runs from Windows NT Servers. Microsoft has the benefit of having access to Real's older streaming codecs (version 4.0 and back) while also including the client (Microsoft Media Player) on all Windows machines to get market penetration similar to Real's. The ASF has recently introduced a number of interactive elements that are similar to SMIL. Microsoft is also supporting the HTML+TIME format which will allow SMIL like timed elements within HTML itself. One of the main disadvantages of Real is that the user must have the plug-in to see it. By building this functionality into the browser Microsoft can introduce the advantages of time-based web development to all web developers. Recently Microsoft and Real have been in disputes over the Media Player taking control of Real's media types and trying to playback RealAudio and RealVideo. Don't expect this dispute to end soon.

RealAudio is a great addition to SMIL. Having the ability to synchronize audio with a graphics slide show and/or text allows for a multimedia presentation even on slower 28.8 kb/sec modems. A 28.8 modem generally allows about 2.2 Kbytes/sec. The RealAudio will occupy about 1Kbyte/sec of this bandwidth. That means if you are doing a slide show style presentation you can load a new graphic every 10 seconds as long as the graphic files aren't over 10K each. To this you can easily add RealText which takes up a negligible amount of bandwidth.

While RealAudio is the best sound format for SMIL you should know that SMIL for the Real G2 Player also supports several other formats. However, a sound file that has been encoded well can be 10 to 20 times smaller than a WAV file. The other formats that can be streamed in SMIL are WAV, AU and AIF. In addition on the Windows platform you can used compressed WAV files. You should always test other sound formats on the Real G2 player before using them. This can be done by opening them from the hard drive and trying to play them back in the G2 Player. In the real world I've found that some uncompressed WAV files won't playback on Mac and UNIX even though they should. I would recommend using WAV, AIF or Au only on intranet environments where bandwidth is much higher.

Contents:

• Techniques for Encoding RealAudio
• The Process of Encoding RealAudio
• Incorporating RealAudio into the SMIL File

Techniques for Encoding RealAudio