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Add Audio to Video
Add music, replace the soundtrack, mix it with the original or add a second track, with a sync offset.
Free, no uploads, no sign-up. Runs 100% in your browser.
How Add Audio to Video works
The video stream is copied without re-encoding; only the audio is processed. Video work runs in ffmpeg.wasm, the FFmpeg toolkit compiled to WebAssembly (GPL build, loaded as a separate engine file of about 30 MB the first time, then cached).
Input: MP4, MOV, WEBM, MKV, AVI, MP3, WAV, M4A. Output: MP4.
How to use Add Audio to Video
- Drop a video onto Add Audio to Video.
- The first run downloads the ffmpeg engine (about 30 MB, once).
- Set your range, format or quality options.
- Process it (progress is shown live), then download.
Tips
- Shorter clips and lower resolutions process much faster.
- Processing speed depends on your CPU; plug in laptops for long jobs.
- Keep the tab in the foreground while encoding.
Add Audio to Video FAQ
- Are my files uploaded?
- No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.
- Is it free? Are there limits or watermarks?
- Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.
- Does it work offline?
- Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.
Related tools
- Mute Video: Remove the audio track from any video.
- Extract Audio: Pull the soundtrack from a video as MP3, WAV or AAC.
- Audio Merger: Join multiple audio files into one track.
- Video Trimmer: Trim and cut clips with a visual timeline, no re-upload.