Add audio to video
Put music or a voice-over on a video. Replace the original sound or mix both, then adjust volume, timing, looping and fade-out.
- 100% free
- Runs in your browser
- No uploads
- Runs on your deviceEvery tool works directly in your browser. No files are uploaded.
- Your privacy mattersYour files never leave your device, so there's nothing for us to store.
- No limitsUse any tool as much as you need. No daily caps, no waiting.
- Completely freeNo signup and no trial to cancel. Ads keep the tools free.
How to add audio to a video
- Add the video. Drop an MP4, MOV, WebM or MKV file.
- Add the audio. Drop an MP3, M4A, WAV, OGG or FLAC file in the second box. A video works too; its sound is used.
- Choose replace or mix, and the volumes. Set where the audio starts and whether it loops or fades out.
- Add the audio and download. Watch the result on the page before downloading.
Settings for common jobs
| Job | Mode | Volumes |
|---|---|---|
| Music on a holiday clip with wind noise | Replace | New audio 100% |
| Background music under a talk | Mix | New 25%, original 100% |
| Voice-over on a screen recording | Replace | New audio 100 to 150% |
| Keep the event sound, add a quiet soundtrack | Mix | New 40%, original 80% |
How the mix is made
Both sounds are converted to 48 kHz stereo, multiplied by their volume and added together. When the sum gets close to the loudest level a file can hold, it's gently limited rather than clipped, so loud moments don't crackle. The fade-out lowers the new audio over the last three seconds of the video.
Common problems
- The music drowns out the voice: use Mix with the new audio at 20 to 30%.
- "Can't decode that audio file": convert it with the audio converter first, or try another browser.
- The audio needs trimming first: cut it with Trim audio, or use the start point setting.
Frequently asked questions
Replace or mix: which should I pick?
Replace removes the video's own sound and uses only the new audio: right for music over silent or noisy footage. Mix keeps the original and adds the new audio on top: right for background music under someone talking. For music under speech, set the new audio to about 20 to 40% and keep the original at 100%.
What if the music is shorter or longer than the video?
Longer music is cut at the end of the video, with a short fade-out if you leave that ticked. Shorter music loops to fill the video, or untick "Loop" to let it end and leave silence (or just the original sound, when mixing).
Can I start the music later, or from its chorus?
Yes. "New audio starts at" is the moment in the video where it begins, for example 0:05. "Start from this point in the audio" skips the beginning of the music, for example 0:42 to start at the chorus.
Is the video re-encoded?
No, the picture is copied as it is, so there's no quality loss and it's quick. Only the sound is created new, as AAC in MP4 and MOV files or Opus in WebM.
Are my files uploaded?
No. Both files are read and combined inside this browser tab.
Can I use any song?
The tool works with any audio file, but posting someone else's music may break copyright rules or get the video muted on social sites. Use music you have the rights to, or royalty-free tracks.