How to merge subtitles

for example, to see them both in original and in your native language

Usually video players allow you to chose a subtitle track to show, but only one. But what if you want to see two subtitle tracks at the same time? For example, when you're learning a foreign language, and want to see text both in original and your native languages at the same time.

Easy!

Run ffprobe Movie.mkv to see what subtitles are available in the movie file.
Find out their indexes - they're 0-based, and not the stream number that ffprobe shows you
For each of subtitle tracks you want to extract, run the following command:
```
 ffmpeg -i Movie.mkv -map 0:s:5 file.srt
```
where 5 is index of the stream, file.srt is the output file with subtitles, and Movie.mkv is, you guessed, the video file. More info about this command available on stackoverflow
After that, use this tool to merge files together: https://subtitletools.com/merge-subtitles-online