Add Music to Video
Drop in a video and an audio track and add a soundtrack in seconds. Replace the original audio or mix it with your new track, loop short clips to match the video length, fade out cleanly, and control volume — all processed locally in your browser with FFmpeg.wasm. Your video is never re-encoded, so output stays fast and lossless.
Use Cases
How to Add Music to a Video
Click "Load FFmpeg Engine" to initialize the in-browser video processor (one-time ~31 MB download, cached after first use).
Drop your video file (MP4, WebM, or MOV) into the first zone and your audio file (MP3, M4A, or WAV) into the second.
Pick Replace or Mix mode, optionally loop the audio to match the video length, add a fade-out, and set the volume of the new track.
Click "Add Music to Video" to process locally, then preview the result and download the finished MP4 — your video track is never re-encoded.
Frequently Asked Questions
- Are my files uploaded?
- No. Both your video and audio files are processed entirely in your browser using FFmpeg.wasm — nothing is ever uploaded to a server.
- What's the difference between Replace and Mix mode?
- Replace mode drops the video's original audio track entirely and swaps in your new music. Mix mode blends your new audio with the video's existing audio track, so both are audible together.
- Does this tool re-encode my video?
- No. The video stream is always copied (`-c:v copy`), never re-encoded, so processing is fast and there is zero quality loss on the video track — only the audio is modified.
- What happens if my music is shorter than the video?
- Enable "Loop audio to match video length" to repeat the track for the full duration of the video. The output is always capped at the video's original length.
- Can I use Mix mode on a video with no audio?
- If the video has no existing audio track, Mix mode has nothing to blend with and will show an error — switch to Replace mode instead, which works with silent videos.
- What audio and video formats are supported?
- Video: MP4, WebM, and MOV. Audio: MP3, M4A, and WAV. Output is always a standard MP4 file.
Replace vs mix — what happens to the original audio
There are only two useful ways to put a track over a clip, and picking the wrong one is the most common reason an edit sounds off. The difference is entirely about what happens to the audio already in the video.
| Mode | Original audio | Result length | Use when |
|---|---|---|---|
| Replace original audio | Discarded entirely | Matches the video | Silent footage, b-roll, screen recordings, anything where the on-camera sound is noise |
| Mix with original audio | Kept and blended under the new track | Matches the video | Dialogue or ambience you want to preserve with music behind it |
- If the music is shorter than the video the audio simply ends; if it is longer it is cut at the video’s end. Trim the track first when you need it to land on a specific beat.
- Mixing two loud sources can clip. If the result sounds crunchy, lower the music before importing rather than after export — clipping introduced at mix time cannot be undone.
- Everything is re-encoded locally with ffmpeg.wasm, so a long clip is bounded by your device’s memory rather than an upload limit.
Related tools
More free, in-browser tools from the Video & Audio set — every one runs locally, with no sign-up and no upload.