Add Subtitles to Video
Embed an SRT subtitle track into your MP4 as a selectable caption track, in your browser. Free, private, no signup or upload.
About the Add Subtitles to Video
This free tool adds an SRT subtitle file to your video as a soft, selectable caption track inside an MP4. Players and platforms that support captions can then turn the subtitles on or off — ideal for making tutorials, interviews and social videos accessible without permanently altering the picture.
Everything runs in your browser using FFmpeg WebAssembly, so neither your video nor your subtitles are uploaded. The engine (about 30 MB) downloads from a CDN on first use and is cached, so the first run is slower than later ones. The subtitles are muxed into the MP4 as a mov_text track, which is reliable and keeps the video stream untouched.
An honest note: this embeds captions as a switchable track rather than permanently burning them into every frame, so a player that ignores subtitle tracks will not show them. If you need the timings first, prepare them with our Subtitle Editor. Files up to 100 MB are supported.
How to Use the Add Subtitles to Video
- 1Choose a video file (MP4 works best), up to 100 MB.
- 2Choose the matching .srt subtitle file.
- 3Click Add Subtitles and wait for the progress bar.
- 4Download the captioned MP4 and enable subtitles in your player.
Frequently Asked Questions
Is my file uploaded to a server?
No. All processing runs in your browser using FFmpeg compiled to WebAssembly. Your file never leaves your device — only the converter engine is downloaded, once.
Why is the first run slow?
The first time you use any converter here, the browser downloads the FFmpeg core (about 30 MB) from a CDN and compiles it. It is then cached for the session, so later runs are much faster.
Are the subtitles burned in permanently?
No — they are embedded as a selectable caption track (mov_text) that viewers can toggle on or off. This keeps the video untouched and the file small, but a player must support caption tracks to display them.
What subtitle format do I need?
An SRT (.srt) file whose timings match the video. You can create or fix timings first with our Subtitle Editor, then add the file here.
Why choose an MP4 video?
The mov_text caption track is designed for MP4/MOV containers, so an MP4 video gives the most reliable, widely-supported result.