Sync Subtitles – Fix Drift and Framerate
When subtitles start in sync but are seconds off by the end — or vice versa — a simple shift will not help. This tool stretches the whole timeline using two reference points, or a framerate conversion, so every line lands where it should. Works with .srt, .vtt and .sbv files; nothing is uploaded.
Accepted: .srt, .vtt, .sbv
Your files never leave your device.
How to use this tool
- Drop your subtitle file on the box above.
- Pick a cue near the start and type the time it is actually spoken; do the same for a cue near the end.
- Check the computed scale and offset, then download the synced file.
Why subtitles drift
Drift almost always comes from a framerate mismatch. A film released on PAL DVD runs at 25 fps; the same film on Blu-ray or a web rip runs at 23.976 fps. Subtitles timed for one version run roughly 4 % too fast or too slow against the other, which adds up to about two and a half minutes over a feature film. Different cuts, inserted logos or removed intros add a constant offset on top. Two-point synchronisation corrects both at once.
Two-point sync in practice
Choose one cue close to the beginning and one close to the end — the further apart, the more accurate the result. For each, watch the video and note the exact moment the line is spoken. Enter those times as the targets. The tool solves the linear mapping t′ = scale × t + offset that maps both cues exactly onto their targets and applies it to every cue in the file, including end times, so durations scale consistently.
If you already know the framerates involved, switch to Framerate mode and pick the source and target rates. Common conversions are 25 → 23.976 (PAL to film), 29.97 → 23.976 (NTSC to film) and the reverse.
Checking the result
A scale close to 1.0427 or 0.9590 confirms a PAL/film mismatch; a scale of exactly 1 means you only needed a shift. Load the synced file in your player and spot-check a line in the middle of the video. If it is still slightly off, run the tool again on the output with a fresh pair of anchors — the operation is lossless apart from millisecond rounding.
Frequently asked questions
- What is the difference between shifting and syncing?
- Shifting moves every cue by the same amount and fixes a constant delay. Syncing also stretches or compresses the timeline, which is needed when the delay grows or shrinks over the course of the video.
- How do I know which framerate my video uses?
- Open the file in VLC and press Ctrl+J (Cmd+J on macOS) to see the frame rate in Codec details. MediaInfo and ffprobe also report it.
- Can I use the first and last cue as anchors?
- Yes, and that is usually the best choice. The tool preselects them. Just make sure you can clearly hear both lines in the video so the target times are accurate.
- Does my file get uploaded?
- No. The calculation is a handful of multiplications performed in your browser. Your subtitles never leave your device.