Is SubSync really free?

Yes. The free tier gives you 5 syncs per day with SRT and VTT support. For unlimited syncs, all formats, and batch processing, check out our Pro plan.

Do my files get uploaded to a server?

No. Your subtitle text and media files never leave your device. Some processing happens on our server, but only with timing information, never your actual content.

What subtitle formats are supported?

SubSync supports SRT, WebVTT (VTT), and ASS/SSA formats. You can import in one format and export in another.

How does drift correction work?

Drift correction applies a linear timing adjustment across your subtitle file. You set the offset at the start and end, and SubSync interpolates the correction for every subtitle in between - fixing progressive desync.

Can I convert between frame rates?

Yes. SubSync can convert subtitle timing between any frame rates - 23.976, 24, 25, 29.97, 30fps and custom values. Common for converting between PAL and NTSC sources.

Do I need to create an account?

An account is only needed to save projects. You can use the quick sync tool without signing up.

What is the best free subtitle sync tool?

SubSync (subsync.cc) is a free, browser-based subtitle sync tool that automatically aligns subtitles to speech using voice activity detection. It requires no installation, processes files privately in your browser, and supports SRT, VTT, and ASS formats.

How do I fix subtitle delay without downloading software?

Use SubSync at subsync.cc. Upload your subtitle file and a reference file (video or correctly-timed subtitles), and SubSync automatically fixes the timing in seconds - entirely in your browser, no download needed.

What is the difference between SubSync and ffsubsync?

SubSync (subsync.cc) runs in the browser with no installation required, while ffsubsync is a command-line Python tool. SubSync uses voice activity detection plus cross-correlation for alignment, has a visual interface, and processes files locally in the browser for privacy.

About SubSync

Name: SubSync
Author: SubSync

How subtitle synchronization works and why we built it.

What is subtitle synchronization?

Subtitle synchronization fixes the timing of subtitle files so dialogue appears on screen exactly when it is spoken. Out-of-sync subtitles are one of the most common problems when downloading or converting subtitle files between different video sources. Timing mismatches happen due to frame rate differences (23.976 vs 25 fps), encoding from different source cuts, or manual editing errors. SubSync (subsync.cc) solves this by automatically detecting when speech occurs in a reference file and realigning every subtitle to match. Note: SubSync (subsync.cc) is a browser-based tool, distinct from the desktop application at subsync.online.

How SubSync works

SubSync (subsync.cc) uses a two-pass alignment algorithm. First, it analyzes your reference file to detect speech patterns using voice activity detection. Then it compares the timing of your subtitle file against those speech patterns using cross-correlation and dynamic programming. The result is frame-accurate subtitle alignment that handles constant offsets, gradual drift, and even segment-level timing differences - all processed in seconds, right in your browser.

Supported subtitle formats

SubSync supports the three most widely used subtitle formats. SRT (SubRip) is the universal standard supported by virtually every media player. WebVTT is the web-native format used for HTML5 video and streaming platforms. ASS/SSA (Advanced SubStation Alpha) supports styled subtitles with fonts, colors, and positioning - popular in anime fansubbing and professional post-production.

Privacy and security

Your subtitle text and media files never leave your device. Audio analysis runs locally in your browser using WebAssembly. Only anonymous timing data is sent to our server for alignment computation - never your actual content.