Converting sub/idx to srt online
Sub/Idx or VobSub format subtitles are usually extracted from DVDs. These subtitles always come in a pair, a sub file that contains picture of the subtitle text, and an idx file that contains information of when to show each picture of text. You need both the sub file and the idx file to use them, the subtitles are unusable if you only have one or the other. This online tool uses OCR to read the text in each picture, and then matches each line of text with the correct timestamp. Converting idx/sub to srt online can take a few minutes, possibly longer if the site is busy. The page will update automatically when the file is done processing. Because it takes a long time to convert a VobSub file, they can only be uploaded one by one, and not inside an archive file.
No idx file
If you have a .sub file, but no .idx file, this tool will not work. But there is a chance that your .sub file is a MicroDVD file because they share the same file extension. To find out if it is a MicroDVD file, you can try converting it using the convert to srt tool.
Sub/idx type subtitles use pictures of text to display subtitles on the screen. This works great if you want your subtitles to work on every tv in the world, regardless of what font or text encoding the tv uses. Using pictures to display the text also has downsides: editing the text is very hard, the files are relatively big, and the display quality can be low (especially on big screens). Nowadays the VobSub format isn't used that much anymore. A lot of newer devices such as smartphones and some smart TVs don't support sub/idx subtitles at all. This converter tool can be used to convert VobSub subtitles to srt so you can use them on any device.
Sub/Idx files can contain multiple languages. This tool will extract every language that is inside the file. It is not possible to only select the specific language you want, so you'll have to wait until all the languages that come before the one you want are done processing.