Hardcode Subtitles into Video (Beta)
The impossible one: real subtitle burning with zero upload. FFmpeg runs inside your browser — your video never touches a server.
Your subtitles and videos never leave your device — everything is processed locally in your browser.
Optional: drop a video for live preview
Your video NEVER uploads — it plays straight from your disk.
Drop the subtitle to burn
SRT, VTT, ASS, SSA or SBV — styled with libass
Beta — encoding runs on YOUR device via WebAssembly. A 10-min 720p clip can take several minutes and needs ~1 GB free RAM. Low-end phones may struggle; keep this tab in the foreground.
Frequently asked questions
Are my subtitle and video files uploaded to a server?
No. SubFix is 100% client-side: parsing, converting, syncing and even burning subtitles all happen inside your browser using JavaScript and WebAssembly. Your files never leave your device.
Which subtitle formats are supported?
SubFix reads and writes SRT, WebVTT (VTT), ASS, SSA and SBV (YouTube), and can also export plain TXT transcripts. Format detection is automatic.
How does hardcoding subtitles work without a server?
SubFix loads FFmpeg compiled to WebAssembly (about 32 MB, only when you use the burn tool) and renders subtitles onto the video frames locally. It works offline once loaded, but is slower than a desktop app — best for short clips.
Is SubFix really free?
Yes — free forever, no sign-up, no watermarks, no file-size games. Because your device does the work, our costs stay near zero.