LumaTool
Local Processing

Merge Subtitles Online

Combine nearby cues in one subtitle timeline using explicit limits.

Runs locallyNo uploadYour input is processed in your browser.
Subtitle Merger online tool preview
Merge Subtitles Online Combine nearby cues in one subtitle timeline using explicit limits.

Subtitle Merger

Merge short subtitle fragments into natural cues while preserving earliest start and latest end times.

What this tool does

This merger combines adjacent cues from one SRT or VTT timeline when their gap, combined length and duration fit the selected limits. It stops at sentence punctuation.

What it measures or changes

  • One SRT or VTT timeline at a time
  • Maximum gap, characters and duration controls
  • Earliest start and latest end retained
  • Output cues regenerated in chronological order

Technical details

  • It merges adjacent cues, not multiple files and not parallel bilingual tracks.
  • Overlapping or distant cues are only combined when the configured constraints allow it; output is reindexed.

Common errors

  • Assuming it aligns two subtitle files.
  • Choosing limits that create overly long cues.

Best practices

  • Use conservative gap and duration values.
  • Review overlaps and reading speed after merging.

Examples

Join fragmented automatic captions.

Input example 
1
00:00:01,000 --> 00:00:02,000
Hello world

2
00:00:02,020 --> 00:00:03,000
LumaTool
Output example 
1
00:00:01,000 --> 00:00:03,000
Hello world LumaTool

It merges adjacent cues, not multiple files and not parallel bilingual tracks.

Reduce overly short adjacent cues.

Input example 
maxGapMs = 300
Output example 
2 cues → 1 cue

Overlapping or distant cues are only combined when the configured constraints allow it; output is reindexed.

Prepare readable cue groups before line breaking.

Input example 
maxDurationMs = 8000
Output example 
1 → 2 → 3

It merges adjacent cues, not multiple files and not parallel bilingual tracks.

Privacy note

Processing happens locally in this browser. Your text or file is not uploaded to LumaTool servers.

How to use

  1. Step 1. Enter or choose one SRT or VTT timeline.
  2. Step 2. Select the options required for this task.
  3. Step 3. Run Merge cues and review validation messages.
  4. Step 4. Copy or download the merged and reindexed subtitles after checking the result.

Real-world examples

Join fragmented automatic captions

Join fragmented automatic captions.

Reduce overly short adjacent cues

Reduce overly short adjacent cues.

Prepare readable cue groups before line breaking

Prepare readable cue groups before line breaking.

FAQ

What input does Merge Subtitles Online accept?

1 00:00:01,000 --> 00:00:02,000 Hello world 2 00:00:02,020 --> 00:00:03,000 LumaTool maxGapMs = 300 maxDurationMs = 8000

How is the result produced?

It merges adjacent cues, not multiple files and not parallel bilingual tracks. Overlapping or distant cues are only combined when the configured constraints allow it; output is reindexed.

Is my input uploaded?

Processing happens locally in this browser. Your text or file is not uploaded to LumaTool servers.

Which options should I choose?

Choose only the options needed to turn one SRT or VTT timeline into the merged and reindexed subtitles; the defaults preserve the least surprising behavior.

Can I use the result immediately?

Review validation messages and compare a representative sample before using the result in production.

Does it work on mobile?

Yes. The workspace and result controls adapt to desktop and mobile browsers.

What should I do when input is rejected?

Assuming it aligns two subtitle files. Choosing limits that create overly long cues.

Is processing private?

Processing happens locally in this browser. Your text or file is not uploaded to LumaTool servers.

Related tools

S

Subtitle Splitter

Split long subtitle cues by length, words, punctuation, and duration with automatic timing.

Video & Subtitle Tools Ready Local Processing No Upload Use Now S

Subtitle Line Breaker

Optimize subtitle line length for one-line or two-line player-friendly display.

Video & Subtitle Tools Ready Local Processing No Upload Use Now S

Subtitle Cleaner

Clean subtitle text, remove tags, normalize whitespace, and keep cue timing.

Video & Subtitle Tools Ready Local Processing No Upload Use Now S

SRT Subtitle Formatter

Repair SRT numbering, blank lines, timestamps, and cue order locally in your browser.

Video & Subtitle Tools Ready Local Processing No Upload Use Now S

Subtitle Time Shifter

Shift SRT and VTT subtitle timings forward or backward locally.

Video & Subtitle Tools Ready Local Processing No Upload Use Now