.QTX File Extension
What is a QTX file?
Component used by Apple QuickTime Player; enables support for additional video codecs and file formats; allows QuickTime to play video files encoded with third-party codecs; must be installed in the correct folder in order to be recognized by QuickTime.
Early versions of QuickTime for Windows store QTX files in "C:\Program Files\QuickTime\QTComponents." QuickTime 7 for Windows stores QTX files in the "C:\Windows\system32\" directory.
In Mac OS X, QTX files are stored in the "/Library/Quicktime/" folder.