 | Designing Web Audio |  |
SureStream
SMIL
RealPix
RealText
RealFlash
Delivering backwards-compatible content
Case study: TechWeb Today
Summary
The RealSystem G2 is a completely re-engineered architecture of the RealMedia system and was built from the ground up to replace the entire line of RealAudio 5.0 encoding and streaming tools. RealNetwork's second-generation platform introduces enhanced streaming features and powerful new media capabilities that allow you to stream multiple media and datatypes, including separate audio, video, image, and text files, in a synchronized presentation. In addition, G2 offers many improvements in the efficiency and functionality of encoding and streaming media files.
RealSystem G2's SMIL-based multimedia may not have the interactive power and graphics sophistication of Flash or Shockwave presentations, but it has the advantage of a huge user base and the ease of creating multimedia with a simple markup language. By copying the SMIL tags in this chapter, you can get up and running with a fairly rich, albeit simple, multimedia presentation. In contrast, Flash packs more power and automatically takes care of complex timeline issues, but it requires learning a whole new proprietary authoring environment. Expect to see Flash used more widely for more complex high-impact presentations, such as movie and game trailers or product demos, and SMIL for more common everyday uses, such as audio slide shows, sound with scrolling text captions, and video news feeds.
The creation of streaming multimedia presentations is accomplished by using a combination of three new XML-compliant markup languages: the W3C's Synchronized Multimedia Integration Language (SMIL) and RealNetwork's RealPix and RealText. Since SMIL is an open standard, there are a wide range of applications that allow you to easily create synchronized multimedia content for RealSystem G2.
Applications that support SMIL authoring include:
As the high-end solution of choice, TAG features all the bells and whistles for quickly producing complex SMIL presentations (http://www.extend.com).
While not as powerful as TAG, VeonStudio is a complete authoring environment for creating interactive broadband content with SMIL and is one of the easiest authoring tools on the market. VeonStudio is free. The VeonServer can be purchased for a small fee (http://www.veon.com).
Falling between TAG and VeonStudio in horsepower, RealProducer Pro packs powerful tools for building SMIL presentations (http://www.realnetworks.com).
SMIL Composer is a freeware authoring tool that allows you to easily add available media types, arrange their layout and sequence, and decide how they are played in your composition. Then, with one click, you can view your SMIL code or preview your composition in your RealSystem G2 Player. Unlike TAG, RealProducer Pro, and Veon, the SMIL Composer does not support the editing of RealPix or RealText files. The tool assumes you have RealPix and RealText files ready to go before you embed them in your SMIL presentation (http://www.sausage.com).
This HTML editing application features a helpful SMIL tag pack for simple SMIL authoring (http://www.allaire.com/products/homesite/).
The extensions in Dreamweaver support embedding SMIL-based RealPlayer objects into web pages. You can download the Dreamweaver extension free from RealMedia (http://www.dreamweaver.com).
This free SMIL authoring tool enables consumers to compose quick slideshows. The RealSlideshow Plus is inexpensive and packs more interesting features (http://www.realnetworks.com).
RealSystem G2 also supports an increased array of file types and formats via the RealTime Streaming Protocol (RTSP) such as JPEG, GIF, QuickTime, MPEG, MP3, MIDI, VIVO, VRML, AVI, WAV, AIF, AU, and Microsoft's ASF (Active Streaming Format). RealSystem G2 also supports other datatypes for specialty applications.
Additional key innovations in encoding and streaming include:
On-the-fly dynamic bandwidth allocation with SureStream. This technology automatically adjusts data transmission rates to match fluctuations in bandwidth conditions. If a listener's bandwidth drops off suddenly, SureStream detects this change and sends a smaller stream to accommodate the lower bandwidth instead of continuing to try and shove an egg through the straw. SureStream alleviates the breaks and pops associated with bandwidth negotiation and rebuffering in RealSystem 5.0, which is a much needed improvement as 5.0 often overestimates the bandwidth throughput of a user's modem.
Vastly improved sound quality with an 80% increase in frequency response over the previous 20 KB 5.0 codecs. The new G2 audio codecs are the first to be developed in-house by RealNetworks. They reproduce higher frequencies better than previous codecs and result in brighter, more realistic audio. The G2 codecs take advantage of new encoding technologies and vastly improved algorithms for compressing file sizes.
Simplified encoding process. In RealSystem G2, one file serves up to six different connection rates. The default bitrate settings are for 28 Kbps, 56 Kbps, single ISDN, dual ISDN, xDSL, and T1. For the T1 setting, select whatever bitrate you want to encode to, with the maximum at 1.2 Mbps. RealSystem 5.0 requires encoding multiple files for bandwidth negotiation.
Faster encoding. The G2 encoder offers audio encoding that is five times faster than with the previous RealEncoder 5.0.
SureStream technology is a vastly improved method for streaming media. SureStream eliminates the breaks in media transmission due to changes in network conditions, such as a drop in throughput from 50 Kbps per second to 20 Kbps. In previous versions, the RealPlayer buffered a certain amount of data in the queue before it began to play. If the connection rate declined, the stream would still play. However, if it played the contents of the queue before the connection resumed, a break in the transmission would occur until more data was received.
G2's SureStream technology makes possible a dynamic bandwidth-detection relationship between the client and server throughout the serving process. When encoding a RealAudio or RealVideo file, the G2 encoder creates several embedded copies of the file at varying discrete data rates. The server then has the ability to dynamically switch streams based on the client's changing bandwidth conditions.
As illustrated in Figure 7-1, if a connection is initially established at 56 Kbps, and then drops to 48 Kbps, the server can detect this change and respond by altering the serving rate, at a preset increment, to accommodate the new connection speed. If the connection rate increases, it can adjust to that rate as well.
A RealAudio or RealVideo file encoded with G2 SureStream will be much larger than it would be if encoded with RealEncoder 5.0. The larger file size reflects the many embedded copies of the file that have been encoded at different bitrates. While G2 .rm files require somewhat larger storage space, they do not require extra bandwidth to stream because only one bitrate version of the file is streamed at any given time. The others simply remain on the server and are employed only if necessary, due to changes in network connections.
As a key broadcasting innovation, SureStream greatly simplifies the delivery of audio and video content to multiple bandwidth connection rates and ensures a high-quality viewing or listening experience free of drop-outs. SureStream will produce a quantum leap in streaming quality on the Web as more and more developers incorporate the G2 technology, especially those who found bandwidth negotiation with the previous RealMedia platform too complex to implement.
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| 6.7. Summary |  | 7.2. SMIL |
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