Add Audio to Video
Put a soundtrack or voiceover under a video.
Everything runs inside your browser. Your files never leave your device.
Drop your files here
.mp4, .m4v, .mov, .webm, .mkv, .mp3, .wav, .m4a, .aac, .ogg, .opus, .flac · they stay on this device
Ask about Add Audio to Video
Questions about what this tool does, which option to pick, or what it can and cannot handle.
This is the one part of the site that uses a server. The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong; the tool itself is not guessing.
About the Add Audio to Video
Putting a different sound under a video covers three quite different jobs, and this handles all of them with two settings.
Replacing is the common one. A silent screen recording needs a voiceover. A clip filmed in a noisy street needs music instead of traffic. Footage of a machine, a pet or a process has sound that adds nothing and a track that adds a lot. The video's own audio goes, the new file's audio takes its place.
Mixing keeps both, with a level control deciding the balance. This is what you want when the original sound carries information — somebody speaking, a demonstration where the noise is the point — and the added track is there to sit underneath. Fifty per cent gives each an equal share; below thirty the new track becomes background, which is usually right for music beneath a voice.
The third job is the mismatch nobody plans for: the sound is a different length from the picture. A three-minute song under a forty-second clip, or a twenty-second loop under two minutes of footage. Repeating the track to the end is right for music and wrong for narration, where the sensible thing is to let it stop, so both are offered and neither is guessed at.
One detail is worth the paragraph: the picture is not re-encoded to gain a new soundtrack. The existing frames are carried into the new file untouched wherever the container permits, and only the audio is built. That is why this finishes far faster than joining or cropping, and why the visual quality is exactly what you started with.
How to use it
- 1Add two files: the video first, then the sound.
- 2Decide whether the new track replaces the original or mixes over it.
- 3Say what should happen if the sound runs out before the video does.
- 4Run it, and listen to the whole thing before sending it anywhere.
Questions
- What order do the files go in?
- Video first, sound second. Both go into the same drop area, and the list shows which is which.
- What audio formats can I use?
- Whatever this browser can play — MP3, WAV, M4A, OGG and usually FLAC all work.
- Can I start the music partway through the video?
- Not directly. Trim the audio first so its beginning is where you want the music to start, then bring it here.
- Why is this so much quicker than the other video tools?
- Because the frames are not rebuilt. Only the sound track is created, and the picture is copied straight across.