Lay a music track under the voice already in a video, at the volume you choose
Processed in your browser. Nothing is uploaded. Updated on 24 Oct 2026.Music under a voice has to sit low enough to hear every word, and stop gracefully rather than mid-bar. This page starts the music at 25% under the video’s own sound at full volume, repeats it if the video is longer than the song, and fades it out over the last three seconds. Change any of those with a slider and hear it before you save; the picture itself is copied, never re-encoded.
Press Choose video, then Choose audio and pick the song.
New audio starts at 25% under Original sound at 100%; move either slider and play the video to hear the balance.
If the audio is shorter is already on Repeat it and Fade out at the end on 3 s, so the song loops and ends gently.
Press Save the video with this sound to get the MP4 with the music under the voice.
This page puts a new sound track on a video: a song, a voice-over, a cleaner microphone recording, or nothing at all. It was built for the job of finishing AI-generated clips for YouTube, where the picture is final and only the sound changes, and for that job the one thing that must not happen is the picture getting worse.
Longer or shorter than the video. Audio that runs past the end of the video is cut at its last frame. Audio that ends early leaves silence, or starts again from the top if you choose Repeat. A fade in and a fade out are there for music.
Keeping the original sound. Set its volume above zero and it stays, mixed under the new track at the level you choose; at zero it is replaced.
The rest of the article, and all 6 questions about Add Audio to Video, are on the Add Audio to Video page.
Drop the video and the music file here and save. The video frames are copied into the new file exactly as they were, not re-encoded, so a 1080p or 4K video keeps every pixel. Only the sound track is new.
Drop the video and the new audio, leave "Original sound" at 0%, and save. The old sound track is dropped and the new one takes its place, lined up where you put it and cut at the video's last frame if it is longer.
Yes. Set Original sound above 0% and the video's own sound stays, with the new audio mixed in at its own volume. For background music under speech, 100% original and 20 to 30% music is a common starting point; a fade-out at the end avoids stopping mid-note.
MP3, M4A, AAC, WAV, OGG, Opus and FLAC, and the sound of another MP4 or MOV. The video must be MP4, MOV or M4V. The result is always an MP4 that plays everywhere and uploads to YouTube as it is.
Still stuck? Ask about Add Audio to Video and anybody who knows can answer. No account needed.
Same job, other tools: YouTube Shorts Editor – Make a 9:16 Short from clips: transitions, your logo and a voice-over, no upload · Change Video Speed – Speed up a video or make slow motion, from 0.25x to 4x, with the sound kept in pitch · Add Logo to Video – Put your PNG logo on a video, bottom right, sized and placed by dragging · Compress Video – Make a video file smaller at a lower bitrate or resolution, right in your browser · Combine AI Video Clips – Join Google Flow, Veo or other AI clips into one video in story order · GIF to MP4 Converter – Turn an animated GIF into a much smaller MP4 video, each frame kept for its own delay.