Add audio to video
Drop a video, choose a song or a recording, and decide whether it replaces the sound or plays under it. The picture is copied as it is, so nothing is lost and it is quick.
Updated November 5, 2026
Options
The picture is copied without re-encoding; only the sound is written again.
How it works
- Drop a video anywhere on this page.
- Choose the sound file under Options, then set where it starts, its volume and fades; press play to hear it with the picture.
- Press Add audio to video and download the result.
When this tool is the right one
You filmed a holiday clip and want a song under it. You recorded your screen and want to add the narration you recorded separately. The wind ruined the sound of a drone shot and a music track would do better. In all three cases you drop the video, pick the sound file and choose Replace or Mix. Replace drops the original track; Mix keeps it and plays the new one under it, which is what a voice-over on a tutorial usually needs.
Because the picture is copied as it is, the job is quick even on a phone: only the sound is written again. The same sound and settings can be added to up to 5 videos in one go, handy for a series of clips that share an intro track.
Getting the levels and timing right
The two dB fields set how loud each track is in the result, from −30 to +12 dB; −6 dB is about half as loud, so a music bed under speech often sits at −12 to −18 dB. Fade in and Fade out, up to 30 seconds each, soften the start and the end so the music does not cut off mid-note. Offset moves the sound along the video: a positive value starts it later, a negative one skips its first seconds.
With Length on Ends with the sound, the video stops where a short track ends, which turns a long clip into a trailer the length of the song.
Formats and what comes out
The video can be MP4, MOV, M4V, WebM or MKV, up to 2 GB; the sound can be MP3, M4A, WAV, OGG, Opus, FLAC or another video. The result keeps the video's own format unless you choose MP4, WebM or MKV; pick MP4 when it has to play on every phone and in every chat app. Nothing is sent anywhere: both files are read and joined in your browser, and the counter under the result stays at zero.
Why people use it
Free, no account
Every tool is free, with no sign-up, no e-mail address and no limit on how often you use it.
Your files stay on your device
The browser opens the file and processes it in memory, on your device. Nothing is uploaded, so nothing can be kept, leaked or looked at.
No watermark
The result is yours as it is: no watermark, no branding, no trial version.
Any device
A phone, a tablet or a computer with a current browser is enough: no app to install, no software to update.
Works offline after the first visit
The browser keeps the pages and their engines, so a tool you have opened once keeps working without a connection.
Open-source engines
The code that does the work is open-source software, named on the Licences page, running as WebAssembly in your browser.
Why it is private
Everything you type or drop here is handled by your browser, on your device. Nothing is uploaded. To verify, open your browser's developer tools, go to the Network tab, and use the tool: you will see no request carrying your data.
While a file is being processed, the counter under the result shows the page's network traffic: 0 requests and 0 B for your data.
How to check it yourself, step by step
What you can check yourself
Open your browser's developer tools on the Network tab before you drop a file: while the tool works you will see no request carrying your data, and the counter under every result shows the page's own measurement.
The site sets no cookies, so there is no cookie banner. Anonymous usage counts and error reports without file names are the only things that leave the page, as the privacy policy describes.
Every change goes through thousands of automated tests in three browser engines, including a guard that fails a test if a single byte of a file leaves the page.
Frequently asked questions
- Is the video re-encoded?
- No. The picture is copied packet for packet, and the result line says so. Only the sound is encoded again, unless you replace it with a track the format can hold as it is, with no volume change, fade, later start or loop: then it is copied too.
- Which sound files can I use?
- MP3, M4A/AAC, WAV, OGG/Opus, FLAC, or the sound of another video (MP4, MOV, WebM, MKV). When the video's format cannot hold that sound, it is converted to one it can.
- What if the music is longer or shorter than the video?
- Longer: it stops where the video ends. Shorter: it stops and the rest is silent, or it repeats to the end (Loop), or the video ends with it (Length: Ends with the sound).
- How do I start the song later, or from its middle?
- Use Offset: 5 starts the sound 5 seconds into the video; -30 skips the first 30 seconds of the sound.
- Is anything uploaded?
- No. Both files are read and joined in your browser; the counter under the result shows 0 bytes sent.
- Can I add music to a video on my phone without installing an app?
- Yes. Open the page in your phone's browser, pick the video and the song from your files, and download the result. Nothing is installed and nothing is uploaded.
- Can I add the same song to several videos at once?
- Yes, up to 5 videos in one list. The same sound, levels, fades and offset are applied to each, and each result is downloaded on its own.
- Will the video get bigger?
- Hardly. The picture is copied unchanged and a new sound track is usually about the size of the old one, so the result is close to the original in size.
- Can I keep the original sound but make it quieter under the music?
- Yes. Choose Mix, then lower Video's sound to −10 or −15 dB and leave Added sound at 0 dB. The original stays audible under the track.
- Why do I not hear the fades when I press play?
- The preview plays the sound with the picture so you can check levels and timing, but fades are not previewed. They are applied in the file you download.
Install it as an app
Chrome, Edge and Android browsers offer to install this site from the address bar or the menu; on iPhone use Share, then Add to Home Screen. It opens like an app, keeps working offline and still processes everything on your device.