How to use
- Add a video and a subtitle file.
- Set font, size, colours, outline, an optional box, and position; the preview draws a real frame with the caption.
- Burn and download.
Worked example
A 1080p clip with white 48 px captions, a 3 px black outline and a 6% bottom margin. On a 720p video the same settings draw 32 px text, because sizes scale with the picture height.
Supported formats and limits
| Input | Video: MP4, MOV, WebM, MKV, Subtitles: SRT, VTT, ASS/SSA, SBV, TTML, JSON |
|---|---|
| Output | MP4 (H.264, audio copied or AAC), WebM (VP9/Opus) |
| Limits | Input files up to 4 GB; the result is built in memory. Every frame is re-encoded, so long videos take a while. Needs a browser with WebCodecs (current Chrome, Edge, Safari 17+ or Firefox 130+). Other browsers are told so before any work starts. |
| Engine | Mediabunny decode → canvas caption renderer (the same code draws the preview) → WebCodecs encode; audio copied when the format allows |
Limitations
- Burned captions cannot be turned off or edited afterwards; keep the original.
- ASS styling (positions, karaoke, per-line fonts) is not used; one style applies to all captions.
- Fonts must be installed on your device; others fall back to a similar font.
Questions
Can viewers turn burned subtitles off?
No. The captions become part of every frame and cannot be turned off or edited afterwards, so keep the original video and subtitle file.
Why does the text look smaller on a 720p video?
Sizes scale with the picture height. Settings that draw 48 px captions on 1080p draw 32 px on 720p, so the captions look the same relative to the picture.
Is the audio re-encoded?
It is copied when the output format allows, otherwise encoded as AAC for MP4 or Opus for WebM. Every video frame is re-encoded.
Guides
Privacy
Runs on your device. Files and text are processed in this browser tab and are not uploaded.
See the privacy policy for how toolsdocks handles data.