Merge Subtitles
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- No upload
- No watermark
Quick answer
Merging subtitles combines two files into one. There are two ways to do it: STACK interleaves both files on the same timeline so overlapping lines show together — the bilingual case, one language above the other — while APPEND places the second file after the first, for joining two parts of a programme. This tool does both in your browser, and neither file is uploaded.
Step by step
How to merge subtitles
- 01
Load both files
Add your two subtitle files — file A and file B. They can be different formats; each is parsed into the same timing model.
- 02
Pick a merge mode
Choose STACK to overlay them on one timeline (e.g. two languages together), or APPEND to run the second file after the first, with an optional gap you set.
- 03
Export the merged file
The combined, renumbered subtitles appear in the preview. Download the single output file or copy it to the clipboard.
In depth
Stack or append — which merge do you want?
The two modes solve completely different problems, so the first decision is which one you are actually doing.
Stack — two files on one timeline
Stacking keeps both files on the same timeline and interleaves their cues by time. Where a cue from file A overlaps a cue from file B, both are shown at once — typically one language stacked above the other. This is how you build a dual-language (bilingual) subtitle track: an English file and a Spanish file of the same video, merged so a viewer sees both lines together.
Append — one file after another
Appending puts file B after file A on the timeline. The whole of the second file is offset to start where the first ends (plus any gap you choose), so the result plays straight through. This is the fix for a film released as CD1 and CD2, or a talk uploaded in two parts, where you have one subtitle file per segment and want a single file for the joined video.
| Stack | Append | |
|---|---|---|
| Timeline | Shared — both files overlap in time | Sequential — B follows A |
| Cues can show together | Yes, that is the point | No, they never overlap |
| Classic use | Bilingual / dual-language track | Join CD1 + CD2, part 1 + part 2 |
| Timing of file B | Kept as-is | Shifted to start after file A |
| You may need to set | Which file goes on top | A gap and file B’s start offset |
A quick way to remember it: stack answers "show me both at the same moment", append answers "play one and then the other". If you find yourself wanting file B to overlay file A, you want stack; if you want file B to wait its turn, you want append. Getting that choice right up front saves you from re-timing later.
How do I make a clean bilingual track?
Use STACK with two files that share the same timeline — the same video in two languages. Decide which language sits on top, and keep an eye on reading speed: two languages on screen at once doubles the text a viewer must read, so consider trimming long lines. To check the result is comfortable, run it through the subtitle timing checker afterwards.
Are my two files uploaded to merge them?
No. Both files are parsed and combined in your browser; the merge is list manipulation done in memory, and the output is built locally. Nothing is sent anywhere — check the Network tab in DevTools to confirm. Translations and unreleased scripts stay on your device.
Related subtitle tools
The inverse operation is split subtitle, which cuts one file into two. If a merged part is out of sync, use the subtitle shifter, and for detailed cue work open the subtitle editor. When the combined file is ready, add the subtitles to your video.
Your files never leave your device
Processed locally in your browser — nothing is uploaded. You can verify it yourself: open your browser’s developer tools, watch the Network tab, and use the tool — no upload request is ever made.
- No file is ever uploaded to a server
- Works offline after the first visit
- No account, no watermark, no limits
A little more clarity
Frequently asked questions
01What is the difference between stacking and appending?
Stacking overlays both files on one timeline so overlapping lines show together — good for two languages at once. Appending runs the second file after the first on the timeline — good for joining two parts of one programme.
02How do I make English and Spanish subtitles show together?
Use STACK mode with the two same-timeline files and choose which language goes on top. Overlapping cues are combined so both appear at the same time.
03I have CD1 and CD2 subtitles for one movie. How do I join them?
Use APPEND mode. Place the CD2 file after CD1 and set it to start at the end of the first segment, adding a small gap if needed, so its timings fall on the right half.
04Can the two files be in different formats?
Yes. Each file is parsed into a common model before merging, so you can combine, say, an SRT with a VTT and export whichever format you choose.
05Does merging renumber the cues?
Yes. The combined file is renumbered in time order on export, so there are no duplicate or out-of-sequence cue numbers.
06Will bilingual stacking make captions hard to read?
It can, because there is twice as much text on screen. Keep lines short and check the result with the timing checker to make sure the reading speed stays comfortable.
07What if the two appended parts overlap slightly?
Increase the gap or set file B’s start offset a little later so its first cue begins after the last cue of file A rather than on top of it.
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