mkvdualsub is a tool for combining two subtitle tracks from mkv file into one combined ass file to display two subtitle tracks simultaneously (one on screen top, another on screen bottom).

Prerequisites:

• mkvtoolnix installed (to see subtitle track information and extract srt files)
• a working internet connection (since subtitles combined by submitting a form to https://pas-bien.net/2srt2ass/ and downloading ass file)

I am using VLC v3 on MacOS for watching videos.

When I decided to improve my English language a bit I found some films in mkv format that had both Russian and English subtitle tracks.

Unfortunately VLC v3 does not allow enabling several subtitle tracks – to simultaneously have both tracks on screen (VLC v4 beta does have this feature, but I had problems with it).

So I am Russian, watching movie with English language audio, looking both on English and Russian subtitles. Like this:

Suppose you have a video file: Gravity.Falls.S01.E01.720p.mkv.

List available subtitle tracks:

mkvdualsub info Gravity.Falls.S01.E01.720p.mkv

Output will be like:

Track ID 5: subtitles (SubRip/SRT)
Track ID 6: subtitles (SubRip/SRT)

Now you can get ass file with combined tracks using:

mkvdualsub join Gravity.Falls.S01.E01.720p.mkv -t 6 -b 5

– where -t sets top subtitle track number, -b sets bottom subtitle track number.

Run video and enjoy combined subtitles (now located inside Gravity.Falls.S01.E01.720p.mkv.ass file in the same directory as video).

If you simply want to join first two subtitle tracks in mkv run:

mkvdualsub join Gravity.Falls.S01.E01.720p.mkv