Subtitle Timecode Fixer & Format Converter Batch shift SRT/VTT/ASS timecodes to fix sync, convert between formats instantly
Positive = delay subtitles (appear later), Negative = advance subtitles (appear earlier). e.g. +500 = delay by 0.5 sec
What is the Subtitle Timecode Fixer & Format Converter?
A free online tool that solves two of the most common subtitle headaches for video creators: 1) Out-of-sync subtitles — batch shift all timecodes forward or backward by any number of milliseconds; 2) Format conversion — convert between SRT, VTT (WebVTT) and ASS/SSA formats. Everything runs locally in your browser — your subtitle content is never uploaded to any server.
Supported subtitle formats
- SRT (SubRip Text) — the most universal subtitle format, supported by virtually all players and platforms
- VTT (WebVTT) — the HTML5 native subtitle standard, used by YouTube, browsers, Vimeo, and most streaming platforms
- ASS/SSA — the most feature-rich advanced subtitle format, supporting custom fonts, colors, and positioning; widely used in anime fansubs
How to calculate the sync offset in milliseconds?
If subtitles appear too late (subtitles lag behind audio) → enter a negative number (e.g. -800 to advance by 0.8 sec); If subtitles appear too early (subtitles ahead of audio) → enter a positive number (e.g. +1200 to delay by 1.2 sec). Tip: pause the video at an obviously out-of-sync moment, note the time difference, then batch-apply the correction here.
For ASS/SSA format, this tool only modifies timecodes in dialogue lines (Dialogue:). Style definitions remain unchanged. Effects styling will be stripped when converting to SRT/VTT — keep a backup of the original file.