RealPix: The SMIL Graphics Format
February 1, 1999
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RealPix is the graphics format developed by Real Networks. It
allows graphics to be streamed over web as part of Synchronized
Multimedia Integration Language (SMIL). RealPix is one of the
many media types that can be played back in the G2 Player from
RealNetworks. Rule will discuss other media types such as RealText,
RealVideo and RealAudio in later articles. SMIL is a
recommendation from the World Wide Web Consortium (W3C) that
allows for the creation of time-based multimedia delivery over
the web.
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In my first article,
Introduction to SMIL, I
gave a broad overview of RealNetworks' implementation of
Synchronized Multimedia Integration Language.
If you haven't read that article, it might be a
good idea to do so now, before continuing with
this more advanced "Part II." In this piece,
we'll focus in on one of the most important
parts of RealNetworks' strategy for using SMIL,
the newly introduced RealPix picture format.
Much like RealAudio and RealVideo, which define
audio and video respectively, RealPix defines
(as you might expect) graphics.
RealPix is not a new graphics format. They are special JPEG files
or GIF files that can be streamed over the net from a Real G2 server.
GIF files can be used unmodified. JPEG files are transformed using
a horrible little program called
JPEGTRAN
that unbelievably still needs to be run from the DOS command line.
There is no Macintosh version available at this time. JPEGTRAN
modifies JPEG files so that if any of the information is lost during
streaming the lost data is randomly dispersed instead of appearing
as continuous blank lines across the image. The JPEGTRAN program
should be placed in the same directory as the JPEG images that you
wish to convert. Start up a DOS window and move to the directory
containing the JPEG files. Once in the directory the JPEG files
can only be converted one at a time using the syntax listed below.
Output.jpg is the new name of the RealPix file and input.jpg is
the current name of the JPEG file. You can not overwrite the old
file.
jpegtran -restart 1B
-outfile output.jpg input.jpg
Yes, it is horrifying that such an important step in SMIL production
must be done one at a time in a DOS window. Fortunately there are
some workarounds. Real does provide a batch conversion capability.
You can run jpegtran.exe in batch mode from the
RealPix Bandwidth Calculator.
For exact instructions on how to run JPEGTRAN from the Calculator click
here.
Some of the third party WYSIWYG tools also contain batch conversion
utilities.
T.A.G. Editor 2.0 - for RealSystem G2
is a good example of such an editor available for both Mac and PC.
Another good WYSIWYG editor is
Veon's V-Active for RealSystem G2.
T.A.G WYSIWYG SMIL Editor
There are some additional tips and tricks I've picked up doing
everyday SMIL production at Discovery Channel. You can use
JPEG files that have not been run through JPEGTRAN. In reality
you will have data loss during streaming that results in a
"black bar" on JPEG maybe once every 1000 downloads.
If this is acceptable you can forgo converting with JPEGTRAN.
The Real G2 Player does not do caching of data. Thus every time
you play the SMIL presentation it must be streamed. Also Real
Pix does not support progressive JPEGs or grayscale JPEG.
Grayscale will display, but the horizontal resolution is cut in
half to produce a very strange image.
RealPix: The RP File
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