Add Music to a Video, Free nothing stored

Replace the video’s sound or mix the music under it

Sound offers Replace or Mix, starting at Replace. Replace drops the video’s own sound, so the music is all you hear: use it for wind noise, chatter, or a screen recording with no sound. Mix keeps the original sound and lays the music underneath, which suits a talking clip, a vlog or a product demo.

Music volume sets the song, and in Mix, Video’s own sound sets what the camera recorded; both start at 100% and can go past it to lift a quiet recording. Two loud tracks added together would clip, so a limiter turns the mix down smoothly at the peaks, linked across both channels so the stereo picture does not shift.

Start time, looping and the two-second fade

Type the moment into “Music starts at”: minutes and seconds such as 0:05 or 1:23.5, or plain seconds. The song begins at that point of the video and always plays from its own beginning. A start time after the video ends gets a message instead of a file.

A song longer than the video is cut where the video ends. A shorter one starts again from the top while “Loop a short song” is on; switch it off and the rest of the video plays without music. “Fade out at the end” lowers the music to silence over the last 2 seconds of where it plays, which is the video’s end or the song’s own end, and never over more than half of that stretch. With the fade off, a song that stops early still gets a 50 ms ramp, because a hard stop clicks.

Pick the video and the song in either order, or use two videos

The tool tells the files apart by what is inside them, not by the order you picked them. The file with a picture is the video; a file with sound and no picture is the music. Dropping the song first gives the same result as dropping the video first.

Two videos work too, for using the sound of one clip under another. The first video keeps its picture and takes the second one’s sound; when only the first has sound, that sound goes onto the silent one. Two sound files, or two silent videos, get a message asking for what is missing.

Why the picture comes out exactly as it went in

The video’s encoded frames are copied packet by packet, with their own timing, rotation flag, and title and date tags. Nothing in the picture is decoded or encoded again, so its resolution, frame rate and quality are unchanged, and no video encoder is needed. Only the new sound is encoded.

The result is exactly as long as the video. Sound encoders pad their last frame, so the final sound packet is shortened to end where the picture ends. Frames before the first key frame are dropped, because no player could show them. The download keeps the video’s name with “-with-music” added.

AAC, Opus and keeping the sound in sync

The new sound is AAC in an MP4 for most videos. A WebM whose picture can stay in WebM keeps that container with Opus sound, and ProRes video goes into a MOV. A browser with no AAC encoder writes Opus instead and says so under the result, because a few phone players skip Opus.

AAC encoders start with a short silent lead-in that some browsers do not mark in the file, which would make the sound play about 44 ms late. The tool measures that delay on your browser and feeds the mix that much earlier to cancel it. MP3 songs carry a lead-in of their own; it is measured for each file against the browser’s own decoding and skipped.

Long videos, large songs and older browsers

The video is checked against your device’s budget: up to 60 minutes and 4 GB on a computer, 15 minutes and 1 GB on a phone. The song is read a little at a time, so even a long one needs little memory; the sound file can be up to 1 GB. A looping song of up to 60 seconds is kept decoded after its first pass, about 23 MB, instead of being decoded again for every loop.

When a browser cannot decode a song piece by piece, the tool falls back to the Web Audio API, which decodes the whole file at once and so takes songs of up to 10 minutes and 300 MB. Surround sound is folded down to stereo. If a file still cannot be read, the message names it and suggests an MP3, M4A or WAV.

Songs you did not make, and when to make your own

Putting a song on a video does not change who owns it. A commercial song you did not make can be flagged, muted or blocked when you post, depending on the platform’s rules and licenses. Music you made, licensed or recorded yourself avoids that question.

When the clip needs music of its own, the paid AI music generator composes a new track from a style you describe. For sounds timed to what happens on screen, such as footsteps or a door closing, the paid AI sound-effects tool adds them in the cloud.

How do you use the add music to video?

1. Add the video and the sound

   Choose both files from your device, in either order. The tool works out which one is the video.

2. Choose Replace or Mix

   Pick Replace or Mix under Sound, then set Music volume for the song.

3. Set the start, loop and fade

   Type when the music starts. Leave “Loop a short song” and “Fade out at the end” on unless you want silence after the song or an abrupt ending.

4. Play it back

   Run it, watch the result with sound, and read Sound, Music and Picture under it before saving.

5. Save your result

   2 free downloads, 8 more after sign-in.

When is the free add music to video enough?

Add Music to Video: questions and answers