Burn subtitles into a video, styled the way you want
Hard subtitles — also called burned-in or open captions — are drawn into the picture itself, so they appear on every phone, TV, website and social app without anyone switching them on. This free tool lets you burn subtitles into a video from an SRT, WebVTT or ASS file, with full control over the font, size, colour, outline, background box and position, and a live preview of any frame before you start.
Most short videos on Instagram, TikTok, YouTube Shorts and LinkedIn are watched with the sound off, and those platforms ignore subtitle tracks inside the file. Burning the captions in is the reliable way to make sure they are seen. The whole job runs in your browser with WebCodecs, so the video is never uploaded.
How to use the Burn Subtitles into Video
- Drop the video on the first box and the SRT, VTT or ASS file on the second. If the video already contains text subtitle tracks you can pick one of those instead.
- Drag the time slider, or use the arrows to jump between subtitles, to preview any frame with the captions drawn on it.
- Adjust font, size, colours, outline, background box, position and margins until the preview looks right. ASS files can keep their own styles.
- Choose MP4 or WebM, a quality level and, if you like, a smaller size such as 720p for faster encoding.
- Press “Burn subtitles”, wait for the progress bar, then watch the result and download it.
Burn Subtitles into Video features
Live, accurate preview
The preview uses exactly the same drawing code as the encoder, scaled to the frame, so what you see is what you get.
Readable by default
White bold text with a black outline at 5.5% of the frame height, inside 6% safe margins — legible on phones and TVs alike.
Line wrapping
Long lines wrap at the maximum line width you choose, and overlapping cues stack instead of overprinting each other.
Basic ASS styles
Fonts, sizes, primary and outline colours, bold, italic, outline width, shadow, opaque boxes, alignment, margins and the \an, \pos, \i, \b, \c and \fs override tags are honoured.
Audio kept
The soundtrack is copied untouched when the output format allows; only the picture is re-encoded.
Private
Decoding, drawing and encoding all happen on your device with Mediabunny (MPL-2.0) and the browser’s own video encoder.
Settings that work well
| Where the video goes | Suggested style |
|---|---|
| Instagram Reels, TikTok, Shorts (9:16) | Size 6–7%, bold, outline 10%, position bottom with a 15–20% margin so captions clear the app’s buttons |
| YouTube and LinkedIn (16:9) | Size 5–5.5%, outline 8%, bottom margin 6%, max width 80–90% |
| Busy or bright footage | Background box behind each line at 60–75% opacity |
| Presentations and tutorials | Size 4.5%, box behind the whole cue, alignment centre |
How burning subtitles works
Every frame of the video is decoded, drawn on a canvas, the subtitles active at that frame’s timestamp are drawn on top, and the frame is encoded again with H.264 (MP4) or VP9 (WebM). Because each frame is re-encoded, the job takes a while — roughly real time or faster on a modern laptop, longer on phones and for 4K video. Choosing 1080p or 720p speeds it up considerably.
Re-encoding always costs a little quality and the text can no longer be turned off or edited. If you only need switchable captions for players such as VLC, Plex or a smart TV, Add Subtitles to Video is instant and lossless. To get an SRT out of an MKV first, use Extract Subtitles.
Fonts and languages
Text is rendered with the fonts installed on your device. Hindi, Tamil, Arabic, Chinese, Japanese and other scripts use the system’s fallback font when the chosen font lacks them, so preview the result. ASS files that name a font you don’t have will fall back to Arial. Advanced ASS effects such as karaoke, fades, rotation, blur and vector drawings are not reproduced.
Burn Subtitles into Video FAQ
How do I burn an SRT file into an MP4?
Drop the MP4 and the SRT here, adjust the style in the preview, keep “MP4 · H.264” selected and press “Burn subtitles”. When encoding finishes, download the new MP4 — the subtitles are now part of the picture.
What is the difference between hard and soft subtitles?
Hard (burned-in) subtitles are pixels in every frame and always visible. Soft subtitles are a separate track viewers can switch on or off. Social apps and many TVs only show hard subtitles.
Will the video lose quality?
Burning subtitles requires re-encoding the picture. “High” quality is visually very close to the original; “Medium” gives smaller files that look fine on phones.
Can I keep the styles from my ASS file?
Yes, basic ones. Tick “Use the ASS file’s own styles” to apply its fonts, sizes, colours, outlines, shadows, alignment and margins, plus common override tags. Animated effects are not supported.
Why is encoding slow on my phone?
Every frame is decoded, drawn and encoded again. Phones have less power, so choose 720p and Medium quality for long clips, and keep the tab open in the foreground.
Is my video uploaded?
No. The video is processed entirely in your browser; nothing is sent to a server.