How to use
- Drop a video file (MP4, WebM, MOV, and more) onto the box or click to choose one.
- Click Select music and pick the audio file (MP3, WAV, M4A, and more) you want as the new soundtrack.
- Click Apply and wait while the new audio is mapped onto your video.
- Download your new MP4 with the replaced audio.
Frequently asked questions
Does the new audio replace the original sound?
Yes. The audio track you choose completely replaces the video's original soundtrack, so only your new music or voice is heard in the exported MP4.
What video and audio formats are supported?
You can load common video formats like MP4, WebM and MOV, and audio files like MP3, WAV and M4A. The output is always saved as an MP4.
How long will the output video be?
The output matches the shorter of the two inputs. If your audio is shorter than the video the result is trimmed to the audio's length, and if the video is shorter it is trimmed to the video's length.
Will re-adding audio reduce my video quality?
No. The video stream is copied through untouched, so the picture stays lossless. Only the audio is re-encoded to AAC for the new soundtrack.
Why is the first run slow?
The first time you use a video tool, a one-time ~30MB processing engine (ffmpeg.wasm) downloads to your browser. It is then cached, so later runs start much faster and even work offline.
Are my files uploaded anywhere?
No. Everything runs locally in your browser with ffmpeg.wasm. Your video and audio never leave your device and nothing is uploaded to any server.
About this tool
Add music to video free and 100% in your browser. Replace a video's audio with your own MP3 or track, export MP4 with ffmpeg.wasm. No uploads, fully private.