Dual subtitle maker: merge two subtitle files into one

How the two files are paired

Most subtitle mergers join cue 1 to cue 1 and cue 2 to cue 2. That breaks the moment two releases split a sentence differently — one file shows a two-line cue where the other has two short cues — and from there every pair is wrong until the end of the film.

This one pairs by time. Each translation line joins the line of your learning file it overlaps the most. A line that overlaps nothing joins the nearest line within one second; beyond that it is left out and counted in the result, so a timing problem shows up before you press play rather than halfway through the film. The file in the language you are learning sets the timing, because it is the one you are reading.

A translation that is early or late by a constant amount needs a shift. One that starts in sync and drifts further out was timed for a different frame rate, and the frame-rate correction rescales it. Watch the pairing count in the result as you adjust either: it rises when the two files come into line.

Which file to download

.srt

For VLC, mpv, Plex, Kodi and most players that accept an external subtitle file. Each cue shows the language you are learning with the translation on the line beneath it.

.vtt

For HTML5 video players and course platforms that ask for WebVTT. The same two lines per cue.

.ass

For players that render styled subtitles, such as VLC and mpv. The language you are learning stays at the bottom and the translation moves to the top of the picture in a different colour, so the two never cover each other.

Anki cards (.txt)

A tab-separated file with one note per paired line: the sentence, its translation and the timestamp. Lines without a translation are left out, because a card with nothing on the back teaches nothing.

When the letters come out wrong

Older subtitle files — Serbian, Croatian, Bosnian, Polish, Russian, Greek, Turkish and Arabic ones especially — are often saved in a Windows code page rather than UTF-8. Read as the wrong encoding, Serbian č turns into è and Cyrillic turns into a run of accented Latin letters.

The tool recognises UTF-8 and UTF-16 by itself. For anything else it guesses between the Central European, Cyrillic and Western European code pages from the bytes, and says so when it guessed. If the preview still looks wrong, choose the encoding by hand. Every download is saved as UTF-8, so the merged file displays correctly from then on.

When you do not need a file at all

On YouTube and Netflix, NoaLingua shows both languages over the player in desktop Chrome with no subtitle file to find. Every word in the line is clickable, a sentence can be saved with its context, and on YouTube the translation is fetched ahead so it is ready when the line appears. See dual subtitles on YouTube and dual subtitles on Netflix.

A merged file is the better route wherever an extension cannot run: a smart TV, a tablet, a media server or a film on your own disk. Why that limit exists is explained in do dual subtitles work on the Netflix app.

Have only one subtitle file and want to read it rather than watch it? NoaLingua’s reader imports .srt and .vtt and turns it into two columns of prose with clickable words. For flashcards, the YouTube subtitles to Anki guide covers the whole sentence-mining route.

Add to Chrome — Free Add to Chrome Opens the Chrome Web Store listing NoaLingua — beyond dual subs: video, web, PDF — free, no account, Chrome 138 or newer.