Sync Subtitles with Your Video
Match two subtitle lines to the speech in your video to correct gradual drift. Your video and subtitle files stay in your browser.
Drop subtitle files here
SRT, VTT, ASS, SSA, SBV, or TXT files. Up to 50 at once.
Your files are processed in your browser and are not uploaded to our servers.
Preview on your video (optional)
Choose a video from your device. Video and captions stay in this tab. MP4 (H.264) or WebM usually works; MKV and other codecs may not play in your browser.
Add a subtitle file first.
What this tool does
This tool fixes subtitles that drift out of sync by matching two lines, one near the start and one near the end, to the right moments in the video. It changes the speed and offset of every line with one linear formula. You can type the two times or pick them while your own video plays in the browser.
How to sync subtitles
- Select Choose files to add subtitles.
- Set Anchor A subtitle number and Anchor B subtitle number, or leave 0 to use the first and last dialogue lines.
- Set Correct time for anchor A and Correct time for anchor B. To capture them from a video, open Preview on your video (optional), choose Video file, select a subtitle, move the video to its matching speech, and select Use current time for anchor A or Use current time for anchor B.
- Select Sync, then check the applied speed, offset, warnings and video captions.
- Select Download or Download all (ZIP).
Options explained
- Anchor numbers refer to the original file. In ASS/SSA, comment rows count toward numbering but cannot be anchors; use the video list to choose dialogue.
- Correct times accept milliseconds, seconds with s, or HH:MM:SS,mmm. Defaults are auto, which leaves the first and last dialogue starts unchanged.
- Apply to defaults to all subtitles. You can select a range by original start times. Anchors define the same transform even if they are outside that range.
- Subtitles before zero trims a crossing line at zero and removes lines ending at or before zero. An alternative removes every line starting before zero.
- The result shows t′ = a × t + b, with b in milliseconds. A warning appears when the speed changes by more than 10%; a matching standard frame rate ratio gets a link to the FPS converter.
Example
With Correct time for anchor A set to 2s and Correct time for anchor B set to 5s, this input:
1
00:00:01,000 --> 00:00:02,000
The gate is open.
2
00:00:03,000 --> 00:00:04,000
Then we can leave.
becomes (a = 1.5, b = 500 ms):
1
00:00:02,000 --> 00:00:03,500
The gate is open.
2
00:00:05,000 --> 00:00:06,500
Then we can leave.
Format notes and limits
- Reads SRT, VTT, ASS, SSA, SBV and timestamped TXT; saves the input format as UTF-8. ASS/SSA round output times to 10 ms. SRT/VTT/SBV and timestamped TXT keep milliseconds.
- Two distinct original times and two matching correct times are required. Each fitted anchor lands within 1 ms internally; the output format can have coarser precision.
- Up to 50 files, 20 MB per file, 200 MB per batch. Times must fit within 1000 hours.
- Video preview uses plain caption text; ASS effects are kept in downloaded ASS files but are not reproduced on the video.
- Captions refresh around the playhead as you play or seek. If a window contains more than 500 subtitles, the video shows the first 500 with a notice; the downloaded file keeps all lines.
- For a constant delay, use Shift subtitles. For a known speed mismatch, use Change subtitle frame rate. For another output format, use the subtitle converter.
Questions
How do I fix subtitles that gradually go out of sync?
Choose one matching spoken line near the beginning and another near the end. Set their correct video times. The tool adjusts the timing between and beyond those points using one speed change and one offset.
When should I shift subtitles instead?
Use Shift subtitles when every line is early or late by about the same amount. Use two-point sync when the delay grows or shrinks through the video. For a known frame rate mismatch, use Change subtitle frame rate.
Do I need to choose a video?
No. You can type both correct times. The optional video preview lets you find each matching moment and copy the current video time into anchor A or B without uploading the video.
What do 0 and auto mean in the anchor settings?
A subtitle number of 0 picks the first dialogue line for A and the last for B, separately for each file. A correct time of auto keeps that selected line's original start. Set both correct times to fix drift.
What if a scene was cut from the video?
One linear adjustment cannot fit several separate cuts. Process a time range at a time and check its boundaries, or use a subtitle editor for multiple local corrections.
Can I sync several files at once?
Yes. The same settings apply separately to each file, and each result has its own preview and warnings. Use a batch when the files need the same correction. Otherwise process them separately.
Last updated October 28, 2026 · Files never leave your browser.