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: The IDX file tells the media player exactly when to show a specific image from the SUB file and where on the screen to place it. 3. Windows Time Travel Debugging (TTD)

: The .sub file contains the actual subtitle images (bitmaps), while the .idx file contains the timestamps and metadata .

(GIS)

(e.g., Adobe InDesign, PDF)

Java archives ( .jar files) sometimes contain an META-INF/INDEX.LIST file, which occasionally bears the .idx extension or relates to indexing mechanisms used by the Java Runtime Environment to optimize class loading.