Language learning
Watch with the original and a translation on screen together, so you can follow both at once.
Subtitle merger
Combine two subtitle files into one.
Stack two languages into a dual subtitle track, or join two parts of a split video. Cues are matched by how much they overlap, so nothing from either file is thrown away.
Browser subtitle merger
Combine two subtitle files.
2cues out
2paired
0unmatched
Merged output
1 cue matched more than one cue from the second file, so those were joined onto one line. Check them for length before you export.
Merging happens in your browser. Nothing is uploaded, and no cue from either file is discarded.
Why merging is not just pairing line one with line one
Two subtitle files for the same video are almost never cut the same way. One language needs two cues where the other needs one, a translator merges a short exchange into a single line, and a reviewer splits a long caption that ran past the frame. Within a minute the cue numbers have drifted apart.
So pairing by position fails. This tool pairs by time instead. The first file provides the timing spine, and every cue in the second file is attached to whichever first-file cue it shares the most screen time with. Two short cues that both fall inside one long cue are joined onto the same line rather than one of them being lost.
Anything that overlaps nothing at all is kept as its own cue and counted for you. If that number is high, the two files are out of sync with each other, and merging will not fix that. Correct the timing first with the subtitle timing shifter, then merge.
What people merge subtitles for
Bilingual audiences
One track that serves viewers who read either language, where the platform allows only a single subtitle file.
A split video
Two parts of one recording, joined with the second file shifted to start after the first.
The thing to check after merging
A merged bilingual cue holds roughly twice the text of a single-language one, in exactly the same amount of screen time. Reading speed therefore roughly doubles, and a file that was comfortable in one language can be unreadable in two. That is the trade dual subtitles make, and it is worth being deliberate about rather than surprised by.
Run the merged file through the subtitle validator to see the characters per second and line lengths you actually ended up with. The reading speed guide explains what the numbers mean and what to do about them.
If you need the second language in the first place, the video subtitle translator produces it while keeping the cue timing, and the translation guide covers what to re-check. Where a platform accepts more than one subtitle track, prefer two separate tracks over a merged one, as the delivery guide explains.
Subtitle merging questions
What does a subtitle merger do?
It combines two subtitle files into one. In bilingual mode both languages appear in the same cue, one line above the other. In sequential mode the second file is shifted to start after the first, for a video split into two parts.
Why do bilingual subtitles come out misaligned?
Because two files for the same video almost never share cue boundaries. One language may split a sentence across two cues while the other keeps it whole, so pairing them line by line drifts. This tool uses the first file as the timing spine and attaches each cue from the second to whichever first-file cue it overlaps most.
What happens to lines that do not match anything?
They are kept as their own cues rather than dropped, and the tool tells you how many there were. A high number usually means the two files are out of sync with each other rather than with the video, which is worth fixing before you merge.
Which file should go first?
The one whose timing you trust, because the first file supplies the cue timing for the merged output. If one file was reviewed against the video and the other was translated from it, put the reviewed one first.
Do merged bilingual subtitles get long?
Yes, and that is the thing to watch. Two languages in one cue doubles the text a viewer reads in the same amount of time, so reading speed roughly doubles too. Check the merged file before you publish it.
Does my subtitle file upload anywhere?
No. The merge runs in your browser. Both files are read locally so you can copy or download the combined file.
Need the second language first?
Generate captions from the video, translate them while the timing stays put, then merge or ship two separate tracks.