Switching language leaves this page. Subtitles and results you have not exported will be lost.
Merge two SRT files into bilingual subtitles
Choose the main timeline and match two languages by time overlap. Review ambiguity before downloading; unmatched cues stay in the output by default.
Two source subtitle files
UTF-8 SRT only; up to 1,048,576 bytes and 3,000 cues per file. Sources stay unchanged; content is processed in this page’s memory.
No file selected
No file selected
Choose two UTF-8 SRT files, set the main and secondary tracks, then start.
Matching summary
After matching, every source cue and its status appears here.
Review and pair cues
Automatic pairs need a unique mutual best and at least 1/2 IoU. Manual choices stay fixed; replacing automatic pairs or pairing below the threshold requires confirmation.
Main subtitles
Secondary subtitles
Choose a cue from the other track
Sorted by exact IoU, then source cue number. Choices below 1/2 require confirmation.
Main timeline output preview
Paired cues use the main timing, with main text above secondary text. Standalone cues keep their own timing; output is sorted by start time.
The actual output appears here after matching and resolving every ambiguity.
Download subtitles
Filename: bilingual-subtitles.srt; UTF-8 without a BOM. Results do not expire automatically. Changing sources, swapping, clearing, or leaving the page clears this job.
Before and after merging
Does it translate subtitles?
No. It only matches two existing subtitle files by time.
When are cues matched automatically?
Only when timeline IoU is at least 0.5 and each cue has a unique mutual best match.
Can I download while matches are ambiguous?
No. Pair each ambiguous cue or explicitly keep it separate before an output is created. If a candidate replaces an automatic pair, the confirmation names that pair; canceling preserves the existing result.
Can I manually pair cues below 0.5 IoU?
Yes, after reviewing the exact ratio and warning. Canceling leaves existing matches unchanged.
Can I keep an automatic match as separate cues?
Yes. The confirmation names the released cue; canceling keeps the original match.
Are unmatched cues discarded?
No. They stay in the output by default; excluding one requires an explicit choice and confirmation. Excluded cues can be restored.
Which subtitle files are supported?
This release defines a strict UTF-8 SRT profile and does not claim support for every SRT variant or player. It accepts LF, CRLF, CR, and one BOM; cue numbers start at 1 consecutively, timecodes have no extra settings, and each cue has nonblank text.
What if too many subtitle cues overlap?
More than 50,000 eligible candidate pairs stops the whole job with a clear prompt to shorten the subtitle segments; no partial result is offered.
Are my files uploaded?
No. Files are processed in local memory without upload, AI, or conversion. Switching language loses the current job. Downloaded files remain under your browser’s and operating system’s control.