Add Music to Video Online
Add your track to a video, either replacing the original audio or mixing the music in with it, and set each volume separately. The music is trimmed to the video's length automatically, and the files never leave your device.
1. Video
Drag a file here or click to select
MP4, MOV, WebM
2. Music
Drag a file here or click to select
MP3, WAV, M4A
Add music to video without uploading either file
The page loads a WebAssembly build of FFmpeg into the browser tab, reads your video and your track off disk and writes the mixed MP4 to your downloads folder, so neither file goes anywhere and there's no cap on how many clips you run. The engine weighs around 30 MB. It's fetched on first use and cached after that, which is why the first export is the slow one.
Replace the sound, or mix underneath it
The two sliders decide which of those you get. Leave the original at zero and the track takes over completely, which is what you want for silent b-roll or a clip whose camera audio is mostly wind noise. Raise it and the two are mixed. A talking-head video usually sits best with the original near full and the music somewhere between 15 and 30 percent, low enough that speech stays clear, and when the music is the point you can set it above the original.
Lengths that do not match
A track longer than the video is trimmed to fit. A shorter one is where people get caught out, because the result depends on the original volume slider. While you're mixing, the clip runs to its natural end and only the original sound is left once the music finishes. With the original at zero the export stops when the track stops, so a 40 second song over a one minute clip gives you a 40 second file. Either pick a longer track and cut it to length with the MP3 cutter, or keep a sliver of the original audio so the video decides the length.
Picture quality, and other tools for the same clip
The video stream is copied straight across, so resolution and frame rate match the source exactly. If the finished MP4 is too big to send, the video compressor takes it down to 720p or 480p. Dead air is better cut with the video trimmer before you add the music than after. For footage you don't have, our AI video models build a clip from a prompt or a still photo on the paid side of the site.
Frequently asked questions
How do I add music to a video?+
Drop in the clip, then an audio file, set the two volume sliders and click Add Music. The result downloads as an MP4.
Can I keep the original sound as well?+
Yes. The original volume slider starts at zero, which replaces the audio outright, and once you push it up both tracks are mixed at the levels you set.
What happens if the music and the video are different lengths?+
A track longer than the clip is cut off where the video ends. With a shorter track it depends on the original volume: above zero the video plays to its full length with only the original sound after the music ends, at zero the export stops where the music stops.
Does the picture get re-encoded?+
No. The video stream is copied into the new file untouched and only the audio is encoded, as AAC, so quality and resolution come out exactly as they went in and the job runs faster than compressing the same clip would.
Why is the first run slower than the rest?+
Mixing audio needs a WebAssembly build of FFmpeg, about 30 MB, which the page downloads the first time you use this tool. After that it's cached and later videos start right away.
Is there a size limit, and is anything uploaded?+
Files over 2 GB are refused, and above 500 MB on a computer or 300 MB on a phone the page warns you that memory may run short. Nothing is uploaded: the video and the track are read from your own disk and the export is written there too.