Streaming Media Metafiles
Part Two: ASX files

In part one of this article series on streaming media metafiles, we discussed what metafiles do and we dove into the details of the RealPlayer metafile format, the .ram file, and some of its useful features. I also described how, while finding the parallels between metafiles and soggy scavenger hunts, I think about work too much. Well, this week I decided to relax a little and bought a hammock. Somehow, I think I’m still getting it wrong. The only action the hammock has seen so far is to be the subject of some sample video I shot for part two of this series on streaming media metafiles. This time, we'll take a look at Windows Media's .asx file format and its capabilities.

.asx files
Like .ram files for RealPlayer, .asx files tell the Windows Media player how to connect to the server to get the media file being requested. This means that at minimum, it needs to contain a URL that points to the server and file that the user wants to play. A basic .asx file looks like this:

<!-- This is a basic .asx file -->
<asx version="3.0">
    <entry>
        <ref href="mms://myserver.com/path_to_movie/myfile.wma" />
    </entry>
</asx>

It's good to note here that the 'version="3.0' attribute of the ASX tag refers to the version of the ASX tagging language itself and not the version of Windows Media Player that will read it. As with any XML format, you can add comments to the file by using the familiar comment tags that work in HTML -- . Unlike XML, the tags are not case-sensitive. If we want to make this example equivalent to our previous .ram file example, we need to add a start time, duration, and a title to our clip. This example will begin playback 5 minutes into the clip and play for three minutes. Remember, using start times to begin playback some minutes into a video file really only applies if you’re streaming from a genuine streaming media server. If you’re serving this from a Web server, the only way to begin playback five minutes into the file is to download the entire first five minutes first (see Streaming vs. Downloading Video: Understanding The Differences)

<!-- This is an .asx file with starttime, duration and title elements --><asx version="3.0"> <title>My Video Title</title> <entry> <ref href="mms://myserver.com/path_to_movie/myfile.wma"></ref> <starttime value="00:05:00"></starttime> <duration value="00:03:00"></duration> </entry></asx>