This article explains what an IDX file is, how to open it, and how to convert it to another file format.
How do I create an idx file?
A file with the .IDX extension can be a movie subtitle file, used to display subtitle text on videos. Sometimes it is called a VobSub file, and it is always accompanied by a SUB file (which contains the actual images that contain the subtitle text) – it describes where and when the images should be displayed.
Other IDX files are used for navigation points of interest, but they have nothing to do with the subtitle format. Instead, VDO Dayton GPS devices store points of interest in the file that the device can refer to during a trip.
Some IDX files are simply general index files that a program creates to reference for faster functions, such as searching through a large number of files. A specific use is as HMI historical log index files that some applications use to run reports.