RealFlash (Designing Web Audio)

7.5. RealFlash

RealFlash provides the ability to stream vector animations made in Macromedia Flash and their associated sound files over the Internet and into the RealPlayer. RealServer is equipped to stream the Flash and audio clips to RealPlayer such that the animation and sound remain synchronized throughout the duration of the stream.

As a rule, RealFlash is best suited for streaming linear presentations that have continuous audio and images synchronized along a timeline. The streaming nature of RealFlash limits the complexity and interactivity that can otherwise be incorporated into non-streaming Flash. Branching and allowing for user-initiated events, such as clicking and rollovers midstream, are not recommended. Movie clips -- series of animations independent of the timeline -- should not be used either.

However, you can add interactivity by using the Shockwave commands play, stop, goto and play, and get URL, after a stream is complete. For example, you may want viewers to be able to click a graphic at the end of a RealFlash presentation that links them to a web page in a browser window. The Shockwave "get URL" command used with this graphic corresponds to an internal RealPlayer command that supports the link.

The nature of vector-based streaming animation is that it does not consume bandwidth at an even rate. At the start of a Flash presentation, images used in the animation are streamed, requiring the heaviest data transfer. After that, only "lightweight" instructions for manipulating the groups and symbols are transferred.

When creating your Flash files, it is recommended that you reduce the bandwidth spikes that correspond to the introduction of new scenes and objects and that may, in turn, cause buffering breaks. RealFlash provides two tools for accomplishing this: the RealFlash Bandwidth Tuner, and the RealFlash BitRate Calculation Spreadsheet, both available for free from RealNetworks.

Here are the basic steps to creating RealFlash:

Import your audio source (WAV or AIFF) into Flash and synchronize it with the animation timeline, thereby creating a soundtrack.
Export your Flash animation to a Shockwave Flash (.swf ) file, creating a compressed version of the animation suitable for streaming. This disables the audio stream.
Export the Flash soundtrack and convert it to the RealAudio format, using the RealEncoder, choosing a codec that fits your clip's bandwidth and content requirements.

When emphasizing complex animation, use low-bitrate codecs targeted for voice. When emphasizing music or narration, use higher-bitrate codecs.

Once you have created your RealFlash file, you can easily incorporate it into a G2 presentation by sourcing it into a SMIL file:

<animation region="flashregion" src="myFlash.swf"/>

To play the Flash animation and its associated audio track together in a G2 show, enclose them together in a set of <par> tags:

<par>
<animation region="flashregion" src="myFlash.swf"/>
<audio src="myFlashAudio.ra"/>
</par>

Additional information on RealFlash is available in RealNetwork's RealSystem G2 Production Guide at http://service.real.com/help/library/guides/production/realpgd.htm.