How to add music to a video
- Drop the video on the left and the song or sound on the right.
- Choose Replace it to swap the video’s sound for the music, or Keep it and mix the music in for background music under voices.
- Optionally set where the music starts in the video, skip the song’s intro, and adjust the two volumes.
- Press Add the sound and download the MP4.
Times can be written as 0:12, 12 or 1:05.5. The line under the settings says in
plain words what will happen: where the song starts, whether it repeats or gets cut, and whether the video’s own
sound stays.
Why the picture does not lose quality
Many online editors re-render the whole video when you add a song: every frame is decoded and compressed again, which takes minutes, softens the picture a little and, on free plans, often adds a watermark. Adding music only changes the sound, so this tool leaves the picture alone. The video frames are copied into the new file exactly as they are, and only the sound track is built new. Afterwards the tool compares every frame of the result with the original, byte for byte, and shows the count.
What we measured
We ran test files through the page in Chrome on a Windows PC (16 October 2026) and read every result with a separate decoder (PyAV):
| Test | Result |
|---|---|
| 60 s, 1080p phone video (60.8 MB) + a song, mixed | 1.7 s; 1,800 of 1,800 frames identical; sound exactly 1:00 |
| 4 s video + 10 s song, Replace | song cut at 4 s with a fade (last 0.13 s at −36 dBFS); old sound gone (−107 dB) |
| Mix with the music at 35% | music sits 9.1 dB under its own level, as set (measured within 0.01 dB) |
| 1.5 s jingle on a 4 s video, starting at 0.5 s | silence until 0.5 s, then the jingle repeats twice to the end |
| Both volumes at 200% | mix peaked at +4.7 dB, lowered by 4.9 dB; decoded result has no clipped samples |
| MKV video + MP3 | MP4 with the picture copied unchanged |
Replace or mix?
Replace is for clips where the original sound is noise: wind, traffic, a crowd, or a screen recording with nothing worth hearing. The music plays at full level and the old sound is removed completely.
Mix keeps what people say and lays the music underneath. When you switch to Mix, the music drops to 35% (about 9 dB quieter) as a starting point, which keeps speech clear on phone speakers. Raise it for a montage with little talking, lower it for an interview. If both are turned up so far that the combined sound would be louder than a file can hold, the tool lowers the whole mix just enough instead of letting the peaks distort, and says by how much.
Fitting the song to the video
- Song shorter than the video: it repeats until the end. Untick Repeat to play it once; the rest of the video is then silent (or keeps its own sound in Mix).
- Song longer than the video: it is cut where the video ends, with a 2-second fade-out so it does not stop mid-note. Untick the fade if the cut lands on a natural ending.
- Skip the start of the music: jumps over a slow intro, so the video starts on the part of the song you want. When the song repeats, it repeats from that point.
- Music starts at: lets the video run on its own sound or in silence first, for example to start the music after an opening line.
Files that work
Videos: MP4, MOV from an iPhone, WebM and MKV. Sound: MP3, M4A, WAV, OGG, Opus and FLAC. You can also drop another video on the right to use its sound, for example a voice-over recorded on a phone. The new file is an MP4 with AAC sound, the combination phones, computers and social apps all accept. An upright phone video stays upright.
Music rights
Instagram, TikTok, YouTube and Facebook check uploads against databases of songs. A commercial song can get the video muted, blocked in some countries or its earnings sent to the rights holder. For anything public, use music you made, have a licence for, or that is offered free to use, such as the YouTube Audio Library. A private video for family is a different matter, but the platforms do not see the difference.
Related: to remove the sound without adding anything, use Mute Video; to cut the song first, Trim Audio; to make a quiet recording louder before adding it, Increase Audio Volume; to join clips before adding one song to all of them, Merge Videos. Everything runs in your browser: neither file is uploaded.