About sup files
Sup files are subtitle files that contain pictures of text. Televisions can show these pictures and not have to worry about text encoding or fonts. The downside to this is that the text in the pictures can't be changed, and that computers usually can't display the subtitles.
Subtitle language for OCR
This tool uses Tesseract OCR to read the text in the pictures, and converts the file to srt. You need to select the language of your sup file for Tesseract to work correctly. If you're not sure what language your sup file is, just give English a try and see if it works.
This tool supports three different sup formats: bluray, hddvd and normal dvd. The code for reading these formats is open source, you can help improve it.