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Tutorial: RealSystem G2 & SMIL

Part 2

RealPix is perhaps the most exciting aspect of G2 technology. The way it works is this: the SMIL file (which makes you smile just saying it) is, to coin a phrase from Brian Meek of Iterated Systems, "the director of the orchestra." It lets the G2 Player know the types of media to prepare for, when and where to display them, and if they are to be displayed concurrently or sequentially.

The SMIL file, written in a form of XML, points directly to the RealMedia files, which are the compressed audio files which will be streamed to the G2 client. The SMIL file also points to the RealPix files, which are also XML-based files that are actually more like scripts, and RealText files, which are simple ASCII text files that contain the actual text, and at the same time tell the G2 Player how to format that text. The RealPix file, in turn, points to the image files which have been specially processed for this use. The RealPix file "instructs" the G2 Player when to show the image, when to fade or swipe it into the next image, when to apply a background color, etc. As a team, the SMIL, RealPix and RealText files come together seamlessly, and provide you with the "presentation." To further understand how the SMIL file works, you may wish to view an image of the SMIL file which illustrates how it "points" to each of the other files.

The G2 Presentation Process

Currently, there are no tools that will enable you to go from start to finish in the production of a SMIL presentation, but there are several that will greatly assist you in that endeavor. First, make sure you have the latest copies of RealNetwork's G2 Player, Encoder and the new SMIL Wizard. To prepare your JPEGs, you'll also need a copy of the JPEGTRAN utility.

Once you've got all your tools at hand, grab yourself a big cup of Java (the type you drink) and hunker down for some Real fun. If you've already got some type of presentation in mind, you can start preparing the basics. First, you must prepare your images for use with RealPix. That involves getting them down to the smallest byte size you can using your current image editor, and saving them in JPEG format (RealPix can utilize both JPEG and the Sting format, but as stated above, at this time JPEG is the only available option).

Now it's time to run the JPEGTRAN utility on them. This prepares the images for streaming across the Net, so that if the transmission is interupted, the Player will know where to restart the transmission. JPEGTRAN was created by The Independent JPEG Group, and is a command line utility (remember those?). You'll need to issue the following string at the command prompt:

jpegtran -restart 1B -outfile output.jpg input.jpg

[Move on to the next part of the article.]

This article first appeared in May, 1998.

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