Fix a constant subtitle delay, then check readability
Use a known reference line, an exact offset and cue-level findings without dropping subtitles.
Two caption problems can look similar: all cues are shifted, or the offset changes across the recording. Inspect both before changing the file. The free shifter applies one declared offset; it does not discover speech boundaries or repair drift automatically.
1. Measure a known line against the right video
Keep the original captions. Choose a clearly identifiable line and note when it should begin in the recording. In an illustrative example, the line begins at 12.000 seconds while the cue starts at 11.250. The needed change is +0.750 seconds.
Check another line near the end. If that line needs the same change, test a uniform shift. If it needs a different change, stop and investigate the media revision, edits or timing source. Read the distinction in subtitle synchronization. Do not keep adding offsets until only the opening looks correct.
2. Preview a copy with an exact offset
Open the subtitle time shifter, paste plain SRT or VTT, and enter 0.750. Positive delays captions; negative moves them earlier. The preview shows all changed times before you download.
To reproduce a boundary check, use the built-in two-cue example and enter -2.000. The first cue would begin before zero, so export stops with a specific cue error. Nothing is silently clipped or removed. A valid 1.250 offset moves its first cue from 1.000–3.500 to 2.250–4.750 seconds and the second from 4.000–7.000 to 5.250–8.250 seconds.
Existing overlaps and unordered start times also need review before this shifter exports. A single offset cannot change the relative spacing between cues.
3. Inspect reading speed independently
Open the reading-speed checker with the same example. Setting CPS to 5 produces two findings: cue 1 at 10.0 characters/second and cue 2 at 13.3. At 20, those two cues produce no findings under that threshold. These are reproducible calculations, not recommendations that five or twenty is correct for every audience.
Characters per second depends on the counting rule. Here spaces and punctuation count, line breaks do not, and the unit is a Unicode code point. Also inspect line length and simultaneous cues. A warning should prompt review, not automatic deletion or an unapproved change of meaning.
4. Watch the final copy
Review wording, speaker information and meaningful non-speech sounds against the recording. Test the beginning, middle and end after importing into the intended player. No checker finding does not mean the captions have been listened to, fact-checked or approved.
Download the corrected file and report without an account. The input remains in browser memory, and the original file is unchanged. For complex styled files, respect the tool's explicit plain-text limitation and keep a workflow that preserves the features you need.
Sources and review date
Format and product references checked October 28, 2026. Guide updated 2026-10-29.
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