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Add Subtitles to Video

Burn SRT, VTT or ASS subtitles into a video, or add them as a track you can switch on and off.

Maintained by BrowserTools · Last updated 2026-11-01

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Most videos are now watched with the sound off: on a phone in public, scrolling a feed, in an open-plan office. Subtitles are what keeps those viewers watching, and they are essential for people who are deaf or hard of hearing and for anyone watching in a second language. This tool puts a subtitle file onto a video. Choose the video (MP4, MOV, MKV, WebM, AVI and most other formats) and the subtitles (SubRip .srt, WebVTT .vtt or Advanced SubStation .ass and .ssa), together or one after the other, and pick how you want them added.

Examples

Input video.mp4 + video.srt
Output video-subtitled.mp4

Burned in: H.264 MP4 with the text in the picture, plays everywhere including social networks.

Input film.mkv + film.ass
Output film-with-subs.mkv

Added as a track in seconds, ASS styling kept, existing subtitle tracks preserved.

Frequently asked questions

Are my video and subtitles uploaded?
No. The tool uses ffmpeg compiled to WebAssembly, which runs inside your browser tab. The files are read from your disk into memory, processed there, and the result is created on your device. Nothing is sent to a server.
What is the difference between burned-in and soft subtitles?
Burned-in (hardcoded, open) subtitles are drawn into the video picture: they always show, on any player or website, but cannot be turned off, restyled or translated later. Soft (closed) subtitles are a separate text track inside the file: viewers can turn them on or off and choose between languages, but the player has to support them, and most social networks ignore them.
Which should I use for Instagram, TikTok, YouTube Shorts or WhatsApp?
Burn them in. These platforms do not read subtitle tracks inside uploaded files, so only burned-in text is guaranteed to appear. YouTube itself also accepts a separate .srt upload in YouTube Studio, which keeps the captions switchable and searchable.
Why does burning subtitles take so long?
Every frame of the video has to be decoded, have the text drawn on it, and be compressed again. In the browser this runs on the processor without hardware acceleration, so expect it to take about as long as the video, and more for 1080p or 4K footage on a phone or older laptop. Adding the subtitles as a track does not touch the frames and finishes in seconds.
My subtitles show empty boxes or question marks. What can I do?
The font does not contain those characters. The built-in Liberation Sans covers Latin, Greek and Cyrillic only. Add a font that covers your script with "Use another font", for example Noto Sans SC or Noto Sans JP for Chinese and Japanese, Noto Sans Arabic or Noto Sans Hebrew. The tool lists missing characters before you start. If accented letters look wrong instead, the subtitle file uses an unusual encoding: open it in the Subtitle Editor, pick the right encoding and save it as UTF-8.
Does burning subtitles reduce the video quality?
Any re-encode loses a little, but at the Balanced setting the difference is very hard to see, and High keeps it practically invisible at the cost of a bigger file. The resolution and frame rate stay the same, and the audio is copied untouched when the source is an MP4 or MOV file.
Which subtitle formats are supported?
SubRip (.srt), WebVTT (.vtt) and Advanced SubStation Alpha (.ass and the older .ssa). WebVTT cue settings and voice tags are dropped, while italic, bold and underline are kept. ASS files keep their own styles, positions and effects when burned in, apart from the font, which is replaced by the built-in or your uploaded one because the browser engine cannot reach the fonts installed on your computer.
Is there a file size limit?
There is no fixed limit, but the whole video has to fit in the memory the browser gives a tab, so files above roughly 1 to 2 GB often fail, especially on phones. For long, high resolution films, adding the subtitles as a track works with much larger files than burning them in. For very large jobs a desktop tool such as HandBrake or ffmpeg will be faster.

About Add Subtitles to Video

Burning the subtitles in, also called hardcoding or open captions, draws the text into the picture itself. It then shows on every device, every player and every social network, from Instagram and TikTok to WhatsApp and a projector at a conference, with no setting for the viewer to find. You choose the look: text size as a share of the picture height, colour, an outline or a semi-transparent box behind the text, bold, top or bottom position and the distance from the edge. A live preview on top of your video shows each line at the right moment, so you can judge the size and position before you start. ASS files keep their own font sizes, colours and positions unless you ask the tool to replace them. Because every frame is changed, the video has to be re-encoded (H.264 in an MP4 file, at the quality you pick), which takes roughly as long as the video plays, or longer for long HD files on slower devices.

Adding the subtitles as a track, also called soft subtitles or closed captions, is the fast alternative: the text is stored next to the video and audio, nothing is re-encoded, and the job takes seconds even for a full film. Viewers can switch the track on or off in players such as VLC, QuickTime, the TV or a browser. You can set the language of the track and whether it is shown by default. MP4 stores it as timed text, which plays almost everywhere; MKV keeps ASS styling intact and also keeps any subtitle tracks the video already had; WebM files get a WebVTT track. Social networks generally ignore subtitle tracks, so for those, burn the subtitles in.

Everything runs in your browser with ffmpeg compiled to WebAssembly: the video and the subtitle file never leave your device, which matters for unreleased work, private recordings and client material. Subtitle files in old encodings such as Windows-1252 are converted to UTF-8 automatically, so accented letters come out right. The built-in font, Liberation Sans, covers the Latin, Greek and Cyrillic alphabets; for Chinese, Japanese, Korean, Arabic, Hebrew, Hindi, Thai and other scripts, add a font file (for example one of the free Noto fonts) and the tool tells you in advance if any character in your subtitles would be missing. If you do not have subtitles yet, the Audio Transcribe tool can write them from the speech in your video, and the Subtitle Editor can fix their timing first.

From title cards to burned-in film subtitles

Silent films told their story with intertitles, cards of text filmed and spliced between the scenes. When sound arrived in the late 1920s, a film could no longer simply swap its cards to travel abroad, and studios first tried shooting the same film several times in different languages. Subtitles were the cheaper answer, and early ones were literally burned in: in the 1930s laboratories in Europe pressed the text onto each frame of the print with heat and chemicals, or etched it away from the emulsion with acid after coating the film in wax. Every copy for every country had to be treated frame by frame.

Television added a second idea. Closed captions, text hidden in the broadcast signal and shown only by viewers who ask for it, were demonstrated in the United States in 1972 and went on air regularly in 1980; in the United Kingdom the Ceefax teletext service carried subtitles on page 888 from the late 1970s. The split between open subtitles that everyone sees and closed ones that the viewer controls is exactly the choice this tool offers today.

The SubRip .srt format comes from a small Windows program of the same name, written around 2000 to pull subtitles off DVDs with optical character recognition. Its plain format, a number, a time range and the text, was so easy to read and write that it became the most widely supported subtitle format in the world, far outliving the program itself.

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