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Toolshed

Add Audio to Video

Add music or a voice-over to a video: replace or mix the sound, set volumes, start time, looping and fade-out. Free, in your browser, no upload.

  • No uploads
  • No limits
  • No signup

Drop the video to add sound to

MP4, MOV, WebM or MKV. Your files never leave this device.

Input:
Video · Audio
Output:
MP4
Runs on:
Your device
Size limit:
None
Account:
Not needed

How to use Add Audio to Video

  1. Add your video

    Drop an MP4, MOV, WebM or MKV file, or click to browse. It stays on your device.

  2. Choose the sound

    Pick an MP3, WAV, M4A or other audio file. Replace the video's sound or mix the two, set the volumes, a start time, looping and a fade-out.

  3. Save the new video

    Press Add audio and download the MP4. It's exactly as long as your video; the sound is cut, repeated or padded to fit.

Why Add Audio to Video on Toolshed

  • No uploads

    Everything runs in this browser tab. Your files never leave your device.

  • No limits

    No file-size caps, no daily quotas. Process as much as your device can handle.

  • No signup

    No account, no email, no watermark.

Frequently asked questions

Can I keep the original sound and add music under it?

Yes. Choose Mix with the video's sound, then lower the music (for example to 30%) so voices stay clear, or turn the video's own sound down instead.

What if the song is longer or shorter than the video?

The result always matches the video's length. A longer song is cut at the end of the video, ideally with a short fade-out. A shorter one repeats when Repeat the sound is on, or ends in silence when it's off.

Does adding audio lower the video quality? Are my files uploaded?

MP4 and MOV videos keep their picture exactly as it is, so it's quick and lossless; WebM and MKV are converted to H.264 MP4. Everything happens in your browser, so neither the video nor the audio is uploaded.

Are my files uploaded anywhere?

No. Add Audio to Video runs entirely in your browser. Your files are processed on your device and are never sent to a server.

Is there a file size limit?

No fixed limit. The only limit is your device's memory. Very large files work best in a desktop browser.

Is Add Audio to Video really free?

Yes. There's no account and no watermark. A short optional ad, or a 20-second wait, unlocks each download. That's how we keep it free.