Bilingual Subtitle Merger: Align Two SRT Files by Time
Two subtitle files, two languages, two different split points. Paste the original and the translation and Lumi pairs each line by time overlap instead of line number, then exports one bilingual .srt you can drop into a player. Everything runs in your browser.
Output
Why time alignment matters
| Why it matters | Details |
|---|---|
| Line numbers do not survive translation | A translator routinely splits one sentence into three cues, or merges two into one. Pairing line 12 with line 12 then drifts out of sync for the rest of the file. |
| Overlap first, proximity second | Each original cue takes the translation cue it overlaps most; when nothing overlaps, the nearest start within the tolerance is used instead. |
| Gaps stay visible | Cues with no translation are reported rather than silently dropped, so you know exactly which lines still need work. |
| Editor-ready output | The exported .srt keeps valid numbering and origin timings and imports into VLC, PotPlayer, Premiere or DaVinci Resolve. |
Questions
- Why merge subtitles by time instead of by line number?
- Because translation changes split points. A translator turning one English sentence into two Chinese cues shifts every following line by one, and index-based merging then produces subtitles that drift progressively out of sync. Matching on timestamp overlap keeps each language attached to the audio it actually covers.
- What tolerance should I use?
- Start at 1500 ms, the default. Raise it when both tracks were produced from the same audio but rounded differently, and lower it when the file has many short cues close together, where a wide tolerance can attach an unrelated line. The unpaired count updates immediately so you can judge the effect.
- Does the merged file work in VLC and video editors?
- Yes. The export is standard SubRip with sequential numbering and the original timings, with the two languages stacked as separate lines inside one cue. That imports into VLC, PotPlayer, Premiere, DaVinci Resolve and most players that support dual-line subtitle rendering.
- Can Lumi produce the translated track for me?
- Yes. The extension translates the live subtitle track of a YouTube or Bilibili video with your own provider key or the managed quota, keeping segmentation and timing intact, so the second file you would otherwise merge by hand does not need to exist.
- Where does my data go?
- Both files are parsed locally and never uploaded.
The extension generates the translation and keeps both languages in sync with the player, with no files to manage.