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Soft subtitles only show up when the player supports them and the viewer switches them on. Burned-in captions are part of the picture, so they appear everywhere. Add a video and a subtitle file, style the text while you watch, and export an MP4 with the captions drawn in.
Processing locally on your device
Overview
Subtitles reach viewers in two ways. Soft subtitles live in a separate file or track that the player draws on top of the video, so viewers can turn them off or switch language. Hard subtitles are rendered into the frames before encoding: they show on every player, social feed and messaging app, but can never be hidden. Burning in is the usual choice for social clips watched with the sound off, for platforms that ignore caption files, and for screens in public places.
The burner accepts SRT, WebVTT and ASS/SSA files, or subtitle text pasted straight into the page. Plain SRT and VTT cues are styled with your settings: font size, text color, bold, and either an outline (color and width) or a solid background box with its own color, opacity and padding. Captions can sit at the bottom or top of the frame with an adjustable vertical margin. ASS files can keep their own styles and positions, or be restyled like any other file.
The preview draws your cues over the playing video using the same proportions as the export, where all sizes scale with the frame height. Exporting is done by FFmpeg compiled to WebAssembly, using the libass subtitle renderer with the bundled Liberation Sans font so the result does not depend on fonts installed on your computer. Every frame is re-encoded to H.264 (CRF 20, which looks transparent for most footage). The audio is copied unchanged when MP4 can hold it, otherwise it is converted to AAC.
Because every frame is re-encoded, burning is the slowest kind of video job in a browser. A 1080p minute can take a few minutes on a typical laptop, so clips longer than about two and a half minutes switch to a faster encoder preset automatically. The first export also downloads the video engine (about 31 MB), which your browser then caches for later use and offline work.
| Style | Looks like | Best for |
|---|---|---|
| Outline | Text with a thin dark border | Films, interviews, clean footage |
| Box, 60–80% opacity | Text on a translucent band | Busy or bright backgrounds, social clips |
| Box, 100% opacity | Text on a solid block | Maximum legibility, accessibility |
| Bold + outline | Heavier, punchier lettering | Short phrases, small screens |
Drop in the video you want to caption.
Add an SRT, VTT or ASS file in the panel, or paste the subtitle text.
Set the font size, colors, outline or background box, and the position.
Play the video to check the styled captions in the preview.
Click Burn subtitles, then preview and download the MP4.
Use cases
Most feed videos start muted. Burned-in captions on Reels, Shorts and TikTok clips let people follow what is said before they decide to turn the sound on.
Make a copy of a talk or product video with translated subtitles drawn in, for platforms, events or clients that cannot load a separate caption file.
Digital signage, kiosks, slide decks and some TV apps ignore subtitle tracks. Hardcoded text is the reliable way to get captions onto those screens.
ASS files often carry carefully placed signs and styled dialogue. Keep the file’s own styles to burn them in as authored.
Pro tips
Answers to common questions about the subtitle burner.
No. The text becomes part of every frame and replaces the pixels underneath. If you might need a clean version or another language later, keep your original file and burn captions into a copy.
Yes, when “Keep the file’s own styles” is on, the ASS styles, positions and override tags are rendered by libass. Fonts are replaced with Liberation Sans, because the engine can only use the fonts bundled with it. Turn the option off to apply your own style instead.
Trimming can copy the compressed video as it is. Burning has to decode every frame, draw the text and encode it again, which in a browser runs at roughly real time or slower for 1080p, depending on your CPU.
The panel shows the pixel size at your video’s height. Captions around 5–7% of the frame height, roughly 55–75 px on 1080p, read well on phones without covering too much of the picture.
Usually not. AAC, MP3, AC-3, E-AC-3, ALAC and Opus audio is copied into the MP4 unchanged. Other codecs are converted to 192 kbps AAC.
No. ToolEnhancer processes files on your own device inside the browser. They are never sent to, stored on or seen by our servers.
Yes. The subtitle burner is free to use with no sign-up, no watermarks and no daily limits.