No upload, 100% local, no account

Add audio to video

Drop a video, choose an audio track, and download the result, everything runs in your browser.

How Add audio to video works

Add audio to video puts a soundtrack onto a clip, drop a video, choose an audio file (MP3, WAV, M4A, AAC, OGG…), and download the result with that audio. You can replace the original sound or mix the new track with it, set the added track’s volume, and either stop at the shorter stream or loop the audio to cover the whole video.

It runs through ffmpeg compiled to WebAssembly. The video stream is copied without re-encoding, so it is fast and lossless, only the audio is encoded to AAC and trimmed to length with -shortest.

Frequently asked questions

Are my files uploaded to a server?

No. ffmpeg compiled to WebAssembly adds the soundtrack in this browser tab, both files are read into memory on your own device and muxed there, copying the video stream untouched (-c:v copy) and encoding the audio to AAC, trimmed to length with -shortest, and the result is offered as a local download. Nothing reaches Sunasty or any third party. Open your browser's DevTools, go to the Network tab and watch: no request carries your files.

Replace vs mix, what’s the difference?

Replace drops the video’s original audio and uses only your track. Mix keeps the original sound and layers your track on top (handy for adding background music under existing dialogue).

What if the audio is shorter or longer than the video?

Choose “stop at the shortest” to end when either stream runs out, or “loop audio” to repeat the track until the video ends.

Will it re-encode my video?

No, the video stream is copied as-is, so there is no quality loss and it is quick. Only the audio is encoded (to AAC).

Does it work offline?

Yes, once the page has loaded. Because the processing happens on your device, you can disconnect from the network and the tool keeps working. This is the clearest proof that your data never leaves your machine.

Is it free? Do I need an account?

It is completely free and requires no sign-up. There are no watermarks, no daily limits and no tracking cookies needed to use the tool.