Subtitle Merger
Combine two or more .srt or .vtt subtitle files into one — merged by time, renumbered, with an optional per-file shift. Runs entirely in your browser; nothing is uploaded.
What this tool does
Got subtitles split across several files — a movie in two parts, or an English
and a translated track you want shown together? This tool merges two or more
SubRip (.srt) or WebVTT (.vtt) subtitle files into one. Every cue from
every file is collected, sorted by its start time, renumbered from 1, and
written back out as a single clean subtitle file. Nothing is uploaded — it runs
entirely in your browser, works offline, and needs no sign-up.
How to use it
- Paste your subtitle files into the box, one after another, with a line
containing only
===between each file (this is how the tool knows where one file ends and the next begins). - Set the Per-file shift if you're joining sequential parts:
- leave it at
0to overlay tracks that already share a timeline (e.g. two languages), or - enter a positive number of milliseconds to push each file after the first further down the timeline (file 2 by the shift, file 3 by twice the shift, and so on) — handy for back-to-back parts like CD1/CD2.
- leave it at
- Choose the Output format —
autokeeps the first file's format, or forcesrtorvtt. - Copy the merged subtitles from the output.
How the merge works
- Mix formats freely. Each file's format is detected on its own, so you can
merge a
.srtand a.vtttogether; the chosen output format is applied to the whole result. - Sorted by time. All cues are ordered by their start time. When two cues start at exactly the same moment, the file you listed first stays first — so an overlaid second-language track lands in a predictable order.
- Renumbered. The output is numbered
1, 2, 3 …regardless of the original cue numbers. - Clamped. A shift that would push a timestamp before the start of the video
is clamped to
00:00:00.
Examples
Two files, overlaid (shift 0), produce a single track ordered by time:
1
00:00:01,000 --> 00:00:02,000
Hello.
===
1
00:00:01,000 --> 00:00:02,000
Bonjour.
→
1
00:00:01,000 --> 00:00:02,000
Hello.
2
00:00:01,000 --> 00:00:02,000
Bonjour.
With a per-file shift of 3600000 ms (one hour), the second file's cues move an
hour later — perfect for appending part 2 after a one-hour part 1.
FAQ
How do I separate the files?
Put a line that contains only === (three or
more equals signs) between each file. Everything between separators is treated as
one subtitle file.
Can I merge an SRT and a VTT together?
Yes. Each file's format is detected
independently, and the combined result is written in whichever output format you
pick (or the first file's format on auto).
My two parts both start at 00:00 — how do I join them end to end?
Use the per-file shift: enter the length of the first part in milliseconds. File 2 is moved by that amount, file 3 by twice it, and so on.
Will it keep multi-line dialogue and styling?
Multi-line cue text is kept as written. WebVTT cue settings (positioning/alignment after the timestamp) are dropped when they have no SubRip equivalent.
Is my file uploaded anywhere?
No. The merge happens locally in your browser, so your subtitles never leave your device, and it keeps working offline once the page has loaded.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool subtitle-merge "1
00:00:01,000 --> 00:00:02,000
First file, first line.
===
1
00:00:01,000 --> 00:00:02,000
Second file, first line."New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/subtitle-merge/?subtitles=1%0A00%3A00%3A01%2C000%20--%3E%2000%3A00%3A02%2C000%0AFirst%20file%2C%20first%20line.%0A%0A%3D%3D%3D%0A%0A1%0A00%3A00%3A01%2C000%20--%3E%2000%3A00%3A02%2C000%0ASecond%20file%2C%20first%20line.&offset_ms=0&format=autoMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.