Subtitle Speed Scaler

The Subtitle Speed Scaler retimes a SubRip file for video that is being played back faster or slower than the speed it was captioned at. Paste the captions into the SRT Content box, enter the playback rate in Playback speed (e.g. 1.1), and every cue is rescaled so it lands on the right moment. The retimed file downloads as a standard .srt.

Speed changes are everywhere in modern video. Tutorial creators publish a 1.1x or 1.25x version to tighten pacing, language teachers slow a dialogue to 0.8x for learners, ASMR and meditation channels stretch material, and podcast video is routinely re-exported at a faster rate. The moment the picture is re-rendered at a new speed, the original subtitle file is wrong everywhere except the first frame - and it gets worse the longer the video runs. Rather than re-timing by hand, creators and e-learning teams use a subtitle speed changer to rescale in one step.

The arithmetic is the inverse of the playback rate: the tool computes a factor of 1 divided by the speed you enter and multiplies both the start and end of every cue by it. At 1.1x that factor is about 0.909, so timings compress and captions arrive sooner; at 0.9x the factor is about 1.111 and everything stretches. Because durations shrink along with start times, cues stay on screen for proportionally the same amount of programme material - worth remembering when speeding up substantially, since a caption that was comfortable to read at 1.0x has genuinely less time on screen at 1.5x. Values are rounded to whole milliseconds, the caption text is never altered, and a missing or zero speed produces a prompt rather than a broken file.

Everything runs locally in your browser, so no video or caption data is uploaded.

• Inverse-speed scaling: the tool multiplies every timestamp by 1 divided by the value in Playback speed (e.g. 1.1), which is the correct relationship between playback rate and caption timing.
• Any speed factor: the field is a free numeric input, so 0.75x slow-downs, 1.25x tightening and 2x speed runs are all handled by the same control.
• Durations scale too: both the in and out point of each cue are rescaled, so display times stay proportional to the material instead of captions overlapping after conversion.
• Text preserved exactly: wording, punctuation and line breaks pass through untouched, so a proofread caption file stays proofread.
• Sensible guard: leaving the speed blank or entering zero returns a request for a speed factor rather than an empty or divide-by-zero result.
• Clean SubRip output: rescaled cues are renumbered and written with standard HH:MM:SS,mmm timestamps that any player accepts.
• No upload: the change subtitle speed online workflow is entirely client side, which keeps unpublished course material and client videos private.

1. Paste the subtitle file that matches the original-speed video into the SRT Content box, or click Load sample to try it with example cues.
2. Work out the speed of the version you are publishing relative to the original - a video re-exported ten percent faster is 1.1, one slowed to three-quarters speed is 0.75.
3. Type that number into Playback speed (e.g. 1.1), using a decimal point rather than a fraction.
4. Press Run; the tool applies the 1/speed factor to every cue and prints the retimed SubRip.
5. Check the last cue in the output against the end of your sped-up or slowed video, since that is where any error in the speed value is most obvious.
6. Click Copy or Download to save the retimed file as .srt, giving it a name that identifies the speed variant.
7. If you sped the video up significantly, read a few captions back at the new rate and shorten any that no longer sit on screen long enough to be read.

Example 1 - a tutorial published ten percent faster. Enter 1.1 in Playback speed (e.g. 1.1), giving a factor of about 0.909.

Before:
1
00:00:10,000 --> 00:00:14,000
Open the settings panel.

After:
1
00:00:09,091 --> 00:00:12,727
Open the settings panel.

The cue arrives sooner and is on screen for 3.64 seconds instead of 4, exactly matching the compressed picture.

Example 2 - a language lesson slowed for learners. With 0.8 entered, the factor becomes 1.25 and the same cue is rewritten as 00:00:12,500 --> 00:00:17,500. Captions now sit on screen for five seconds, tracking the slower speech and giving students more reading time - a small change that makes the slowed version genuinely usable rather than merely quieter.

• Publish speed variants confidently: a faster or slower edit can ship with captions that actually match, instead of a subtitle track that is wrong from the first minute.
• No manual re-timing: one number replaces the tedious job of dragging every cue in an editor, which makes speed variants economical to produce at all.
• Keeps accessibility intact: viewers who depend on captions are not excluded from the alternative-speed version of your content.
• Protects your wording: since only timestamps change, approved translations and carefully proofed transcripts carry over untouched.
• Reversible in one step: entering the inverse speed restores the original timings, so a mistake costs a click rather than a rebuild.
• Private and free: unlisted course material and client drafts are converted in your own browser with no upload and no account.