Add Audio to Video
Media & Video StudioLay a music or voiceover track over a silent or existing video.
What is Add Audio to Video?
Add Audio to Video lays a music track or voiceover over a clip by combining two files — your video and a separate audio file — into one MP4. The video track is copied untouched while the new audio is encoded to AAC, and the result is trimmed to whichever of the two is shorter. The original audio in the video is replaced by the track you add. Everything runs locally with in-browser FFmpeg (WebAssembly), so neither file is ever uploaded.
How to use Add Audio to Video
Add your video
Drag the video onto the first drop zone or click to browse. MP4, MOV, and WebM work best. The in-browser video engine starts loading as soon as the video is added.
Add an audio track
In the Audio track panel, drop an MP3, WAV, or other audio file. This becomes the new soundtrack — it replaces the video's original audio rather than mixing with it.
Combine the two
Click Add audio to video. The video stream is copied as-is, the audio is encoded to AAC, and the output is cut to the shorter of the video and audio lengths.
Preview and download
Play the combined clip in the built-in preview to check timing, then download the MP4. Both files are processed on your device — nothing is sent to a server.
Common uses
- Add a background music track to a silent clip or slideshow
- Lay a recorded voiceover over screen-capture footage
- Replace noisy on-camera audio with a clean studio recording
- Set a product or promo video to a licensed music bed
- Attach narration to a demo or tutorial
- Give a montage a soundtrack without opening a full editor
Why choose FreeTools
100% private
Your files are processed inside your browser and are never uploaded to a server.
Free, no account
No sign-up, no watermark, no paywalled “premium” tier. Just open a tool and use it.
Instant
No upload, no queue, no server round-trip — work starts the moment you drop a file.
Runs in your browser
Built on open web standards. Works on any modern desktop browser, nothing to install.
No upload size caps
Nothing leaves your device, so there’s no server file-size limit — only your machine’s memory.
Yours to keep
Results download straight to your device in clean, standard file formats.