Free · Runs in your browser
Pick a video and an audio file, decide whether the new sound replaces the original or plays underneath it, and download the finished clip. The tool is free to use, runs entirely in your browser, and accepts MP4, MOV and WebM videos up to 150 MB and 3 minutes long, plus audio files up to 30 MB. You control where the audio starts, which part of it plays, the fades, looping and both volumes.
Put a soundtrack or voice-over under a clip without installing software, opening a project file or paying for an export.
There is no payment step, no credits and no watermark on the result. The only limits are the file sizes and the three-minute length shown next to the file pickers.
Swap the original track for your music or narration, or keep the original sound and lay the new audio over it. Each volume is set separately between 0 and 100 percent.
Start the audio at any point of the video, trim it with two handles, add fades of up to 10 seconds at either end, and decide whether a short track loops until the video ends.
Decoding, mixing and encoding all happen inside the browser tab. Your video and audio are never uploaded, so private footage stays on your computer or phone.
Four steps take you from two files to a finished clip.
Choose or drop an MP4, MOV or WebM video of up to 150 MB and 3 minutes, then an MP3, WAV, M4A, AAC, OGG, Opus or FLAC file of up to 30 MB. Both show a preview, and you can play the audio before going on.
Pick between replacing the original sound and mixing with it. Set the volume of the added audio, which starts at 70 percent to leave headroom, and in mix mode the volume of the video's own sound.
Move the start slider to decide when the audio begins, drag the trim handles to pick the section you want, set the fades and switch looping on or off. A line below the settings says whether the audio fits, repeats or gets cut at the end.
Press Add audio to video. A progress bar shows the work and a cancel button stops it at any moment. When it finishes, play the result on the page and download it. Changing any setting clears the result, so you never save an outdated file.
Lay a music bed under a promo or a short edit, start it a few seconds in so the opening shot breathes, and fade it out before the final frame.
Add a licensed track to a product demo recorded without sound, or mix a voice-over with the ambient noise of the shoot at a lower volume.
Match a track to a vertical clip, loop a short beat so it covers the whole video, and keep the file in the same MP4 format you started with.
Narrate a WebM screen capture by replacing its silence with a recorded voice-over, trimmed to begin on the exact sentence you need.
Cover wind or crowd noise by replacing the sound with music, or turn the original down and mix a track beneath it. MOV clips from phones work when they use H.264 or HEVC video.
Add quiet background music to a tutorial, or swap a noisy recording for a clean narration track recorded separately.
Video must be an MP4 or MOV with H.264 or HEVC, or a WebM with VP8 or VP9, up to 150 MB and 180 seconds. Audio can be MP3, WAV, M4A, AAC, OGG, Opus or FLAC up to 30 MB. Other codecs, such as AV1, are refused with a clear message.
The picture is copied from your file without re-encoding. The new sound is rendered as 48 kHz stereo and encoded as AAC for MP4 and MOV or as Opus for WebM, at medium quality. Extra audio and subtitle tracks are not carried over.
Add only music, recordings and sound effects that you own or are licensed to use. A clip published with someone else's song can be muted or removed by social platforms, whichever tool made it.
Yes. Using it costs nothing, it adds no watermark, and it never asks for a card or credits. All you need is a browser that can decode your files.
No. Both files are read and processed inside your browser tab, and the finished video is built in memory on your device. Closing the tab discards the result unless you have downloaded it.
Videos can be MP4, MOV or WebM. Audio can be MP3, WAV, M4A, AAC, OGG, Opus or FLAC. The result uses the same container as your video, so an MP4 stays an MP4.
Yes. Choose the mix option, then set the volume of the added audio and of the original sound separately. If the video has no sound track, the tool tells you so and you can switch to replacing instead.
The tool copies the picture rather than re-encoding it, so it only takes codecs that the container can carry: H.264 or HEVC in MP4 and MOV, VP8 or VP9 in WebM. Files over 150 MB or 3 minutes are also refused.
The picture is copied as it is, so its quality does not change. The sound is decoded, mixed and encoded again at medium quality, which is why the file size can differ slightly from the original.
With looping on, a shorter track repeats until the video ends. With looping off it plays once and the rest of the video has no added sound. A longer track is cut at the end of the video.
Fade in and fade out each go up to 10 seconds, and together they cannot be longer than the time the audio actually plays. The sliders adjust themselves when you change the start point or the trim.
The whole soundtrack is mixed in memory before it is encoded, which takes tens of megabytes for a three-minute clip on top of the files themselves. Close other tabs or use a shorter or smaller video.
No. The tool opens on this page and works without an account. Your settings are not saved after you leave, so download the result before closing the tab.
Generate videos from text or images with BestAIVideo's AI video generator, then bring them back here to add your own soundtrack.
