NITE XML Toolkit - How to Play Media Signals

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NXT plays media using JMF (the Java Media Framework). JMF's support for media formats is limited and it depends on the platform you are using. A list of JMF supported formats is at http://java.sun.com/products/java-media/jmf/2.1.1/formats.html. This list is for JMF 2.1.1, which NXT currently ships with.

There are several ways of improving the coverage of JMF on your platform:

• Mac media Using FMJ we have devised a way to pass media control through to Quicktime where it is installed on a mac so that any file that plays using QuickTime on mac, can be used in NXT. See the .command mac startup scripts that ship with NXT for CLASSPATH details.
• Performance packs from Sun - these improve codec coverage for Windows and Linux, and are available from the JMF download page. In particular, note that MPEG format isn't supported in the cross-platform version of JMF, but it is in the performance packs.
• Fobs4JMF for Windows / Linux / MacOSX is a very useful package providing Java wrappers for the ffmpeg libraries (C libraries used by many media players which have a wide coverage of codecs and formats). Download; information. Make sure you follow the full installation instructions which involve updating the JMFRegistry and amending your LD_LIBRARY_PATH. There may still be some compatibility issues with Java 1.5.
• MP3 - There's an MP3 plugin available for all platforms from Sun

Note: direct playback from DVDs or CDs is not supported by JMF.

NXT comes with a cross-platform distribution of JMF in the lib directory, and the .bat/.sh scripts that launch the GUI samples have this copy of JMF on the classpath. On a Windows machine, it is better to install JMF centrally on the machine and change the .bat script to refer to this installation. This will often get rid of error messages and exceptions (although they don't always affect performance), and makes JMF able to find more codecs.

It is a good idea to produce a sample signal and test it in NXT (and any other tools you intend to use) before starting recording proper, since changing the format of a signal can be confusing and time-consuming. There are two tests that are useful. The first is whether you can view the signal at all under any application on your machine, and the second is whether you can view the signal from NXT. The simplest way of testing the latter is to name the signal as required for one of the sample data sets in the NXT download and try the generic display or some other tool that uses the signal. For video, if the former works and not the latter, then you may have the video codec you need, but NXT can't find it - it may be possible to fix the problem by adding the video codec to the JMF Registry. If neither works, the first thing to look at is whether or not you have the video codec you need installed on your machine. Another common problem is that the video is actually OK, but the header written by the video processing tool (if you performed a conversion) isn't what JMF expects. This suggests trying to convert in a different way, although some brave souls have been known to modify the header in a text editor.

We have received a request to implement an alternative media player for NXT that uses QT Java (the QuickTime API for Java) rather than JMF. This would have advantages for Mac users and might help some PC users. We're currently considering whether we can support this request.

 

Last modified 07/02/08