Subtitle Timestamp Shifter

Choose a Correction Mode

Fixed offset adds one positive or negative value to every cue's start and end time. Positive values delay subtitles; negative values advance them.

Linear drift correction uses Offset at the first cue and Offset at the last cue's end. The first label describes the value at timeline time zero; it is not necessarily the offset applied to the first parsed cue. Each cue's start and end offset is interpolated from its own original timestamp, so the cue receives the exact start value only when that timestamp is zero.

The reference point is the end time of the last parsed cue. For each timestamp, the tool uses appliedOffset(t) = startOffset + (endOffset - startOffset) x (t / lastCueEnd), with the interpolation factor clamped to the 0 to 1 range. Offset fields accept seconds, decimals, or values such as HH:MM:SS.mmm.

Shift Subtitles and Review the Result

1. Choose a mode: fixed offset for a constant shift, or linear drift correction for an interpolated offset across the timeline.
2. Enter the offset value(s): as seconds (decimals allowed, e.g. -1.5) or as HH:MM:SS.mmm.
3. Add your subtitles: use Paste subtitle content below, Drop a subtitle file here, or browse files. The file picker accepts .srt, .vtt, and .txt. SRT and VTT extensions identify the format; other pasted or selected content is treated as WebVTT only when it begins with WEBVTT, otherwise it defaults to SRT.
4. For pasted or detected SRT content, use timestamps such as HH:MM:SS,mmm. WebVTT timestamps use HH:MM:SS.mmm, with hours optional when parsing.
5. The offset or drift correction is applied automatically whenever the subtitle content or correction settings are usable.
6. Review the preview: Before & after preview shows each cue's original and shifted timestamps, text, and any negative-time or overlap flags.
7. Download: export the shifted file after successful processing. The generated filename is shifted.srt or shifted.vtt.

Click Clear to remove the current subtitle input and result.

When an uploaded file exceeds 300000 characters, the textarea shows a truncated preview. The full file remains available for processing.

Review Flags and Download the Result

The Before & after preview shows original timing, shifted timing, cue text, and cue-level flags. The tool flags negative timestamps and cues that overlap the next cue after shifting. These flags warn about issues in the shifted output; they do not block Download after successful parsing and shifting. Processing errors do prevent downloading.

Output Limitations and Processing Details

• Cue order and cue text are preserved.
• WebVTT cue identifiers and cue settings are serialized for parsed cues.
• The WebVTT header is retained in the output.
• SRT identifiers are regenerated as sequential numbers.
• WebVTT NOTE, STYLE, and REGION blocks are skipped during parsing and are not included in the download.
• Subtitle files require strict SRT or WebVTT timestamp syntax.

Fix Processing Errors Before Downloading

Correct the input when processing stops. Empty input, malformed timing lines, invalid timestamps, reversed cue times, missing subtitle text, missing timing lines, invalid offsets, and files with no parsed cues produce an error. WebVTT input must begin with WEBVTT on the first line. Errors hide the workspace and prevent Download until the problem is corrected.

Privacy and Local Processing

The implementation reads selected files with FileReader, processes the content in your browser, and creates the download with a Blob. The directly imported implementation contains no upload logic.

Frequently Asked Questions