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Add Audio to Video

Put music, a voice-over or any MP3 onto a video — replace the original sound or mix both, free and private

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100% private. Your file is processed locally in your browser with WebAssembly — it is never uploaded to a server, stored, or seen by anyone.

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Add Audio to Video lets you put a music track, voice-over, sound effect or any audio file onto a video clip. Choose Replace to drop the original sound and use only the new audio, or Mix to keep the original at a volume you set and layer the new track on top — ideal for background music under speech. If the audio is longer than the video it is trimmed to fit; if it is shorter, the video simply continues without it.

The video stream is copied without re-encoding, so the picture keeps its exact original quality and the job finishes in seconds even for long clips; only the audio is encoded to AAC. Everything runs locally in your browser with ffmpeg.wasm: no upload, no account, no watermark. Accepts MP3, WAV, M4A, AAC, OGG, FLAC, Opus and WMA as the audio source.

Why use this tool

No quality loss

The picture is stream-copied; only the audio track is encoded.

Replace or mix

Clean swap, or layer music under speech with an adjustable original-volume slider.

Seconds, not minutes

Without video re-encoding even long 4K clips finish almost instantly.

Private by design

ffmpeg.wasm runs on your device — nothing is uploaded, no account needed.

How to use the Add Audio to Video

  1. Upload the video

    Drag and drop the clip or click to select it; it opens locally in your browser.

  2. Choose the audio file

    Pick the MP3, WAV, M4A or other audio you want to put on the video.

  3. Replace or mix

    Replace uses only the new audio; Mix keeps the original sound at the volume you set.

  4. Add and download

    Click Add Audio — the video is copied without re-encoding and the new soundtrack is muxed in. Download the MP4.

Popular use cases

  • Putting background music under a travel or product video.
  • Adding a recorded voice-over to a silent screen recording or tutorial.
  • Replacing a noisy original soundtrack with a clean studio track.
  • Attaching a licensed jingle or sound effect to a short social clip.

Frequently asked questions

Is it free and are my files uploaded?
It is free, with no signup and no watermark. No. Everything runs in your browser with ffmpeg.wasm (WebAssembly); the file never leaves your device, nothing is uploaded or stored.
What is the difference between Replace and Mix?
Replace throws away the original soundtrack and uses only the audio file you added. Mix keeps the original at the volume you choose (30% by default) and layers the new audio over it — use it for background music under a voice or ambient sound.
What if the music is longer or shorter than the video?
Longer audio is cut to the length of the video. Shorter audio ends early and the rest of the video plays silently (in Mix mode the original sound continues). To loop a short track, join it several times with the audio merger first.
Does adding audio reduce video quality?
No. The video stream is copied bit-for-bit (no re-encoding), so quality, resolution and frame rate are identical to the source. Only the audio is encoded, to AAC at 192 kbps.
Which audio and video formats are supported?
Audio: MP3, WAV, M4A, AAC, OGG, FLAC, Opus, WMA. Video: MP4, MOV, MKV, WebM, AVI, M4V, FLV, WMV, MPG and 3GP can be loaded; the result is saved as MP4.
Can I add audio to a video that has no sound?
Yes — that is the most common case for screen recordings and silent clips. Both modes work; with a silent source the result is the same as Replace.
How do I add a voice-over recorded on my phone?
Record the voice-over (our online voice recorder saves MP3), then load the video here, choose the recording as the audio file and pick Mix with the original at 10–20% if you want to keep some ambient sound, or Replace for a clean narration.
How long does it take?
Because the video is not re-encoded, most clips finish in a few seconds regardless of resolution; only the audio length matters.

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