Free Add Music to Video

Worked example

Press "Try a sample" on the empty page. The chip reads "Making a sample…" for a moment, then a 6-second 640×360 clip called sample-video appears under "Your video" and a 4-second song called sample-music.wav under "Music or audio". The clip ends in .mp4 or .webm, depending on what your browser can record. The clip normally has a quiet tone of its own, so "The video’s own sound" offers "Replace it" (selected) and "Mix it with the music". "Music volume" starts at 80% and "Fade out at the end" at "2 s". The song is shorter than the video, so "Repeat it until the video ends" is selected and the bar under the settings is labelled "music repeats". Press "Add music to video". The page then says "Music added", shows the file size, and the button becomes "Download MP4".

Which settings to use, and the limits

• Add the video first, then the music. The first box is "Your video" and the second is "Music or audio". Under the second box, "No song file? Choose a video instead and its sound is used." means a video dropped there lends its soundtrack, such as a saved Reel or a screen recording. The music box also takes common audio files such as MP3, M4A, WAV, AAC, OGG, Opus and FLAC. Each box holds one file, and the remove button on the file chip empties the box. Each file is checked as soon as it lands. Its length appears beside the file name, with the picture size for a video and "no sound" for a silent one.
• Choose Replace or Mix for the video's own sound. "Replace it" drops the video's own sound, so only the music is heard. "Mix it with the music" keeps it and plays the music underneath, which suits a video with a voice. Mix adds an "Original sound volume" slider beside "Music volume". Both run from 0% to 200% in 5% steps. The music starts at 80% and the original sound at 100%. Mix uses the video's first sound track. If the video has no sound, the choice is not offered and the page says "This video has no sound of its own, so the music becomes its soundtrack."
• Time the music with the two start boxes. "Music starts at" is seconds into the video. "Start the song from" is seconds into the song, to skip an intro. Both start at 0. Type 12, 1.5, 1:05 or 0:01:05; a comma also works as the decimal point. "Use video position" and "Use song position" copy the current time of the players, rounded to a tenth of a second, so you can pause at the right moment instead of typing. Text it cannot read turns the box red and shows "Type seconds, like 12 or 1.5, or minutes and seconds, like 1:05." The main button stays greyed out until that is fixed.
• Decide what happens when the lengths differ. If the song is shorter than the video, "When the music ends before the video" appears. "Repeat it until the video ends" loops the song, and "Play it once" leaves the rest silent, or only the video's own sound in Mix. If the song is longer, the page says "The music is longer than the video, so it stops where the video ends." and the sound always ends with the picture. "Fade out at the end" offers "Off", "1 s", "2 s", "3 s" and "5 s", starting on 2 s. "Fade in (1 s)" is a tick box, off at first.
• Know when the picture is copied and when it is re-encoded. H.264, HEVC, AV1 and MPEG-4 pictures go into an MP4 untouched, so the quality is the original's and the job is quick. Only the sound is encoded, as AAC at 192 kbps. Other video, such as WMV or MPEG-2, is re-encoded to H.264, which takes longer, and the note on the page says so. A WebM with a VP8 or VP9 picture, such as a browser screen recording, also gets a "Save as" choice. "MP4" re-encodes the picture and plays everywhere. "WebM" keeps the picture unchanged, is faster, and uses Vorbis sound. HEVC pictures are tagged so that QuickTime and iPhones can play them.
• Check the size warnings before a long video, especially on a phone. The tool estimates the finished file before you start. Above about 1.75 GB it holds the button and shows "Compress" and "Trim" shortcuts. Above 400 MB on a phone, or 1 GB on a computer reporting 4 GB of memory or less, it shows a warning instead. A memory check can then show "This may be too much for this device" with "Continue anyway" and "Cancel". Your files are processed in the browser and are not uploaded.

Common problems and how to fix them

It says "Processing cancelled."

You pressed "Cancel" under the progress bar. Cancel stops the media engine at once and drops the half-made file, so the words appear in the red message box although nothing is wrong. Both files stay in their boxes with your settings, so press "Add music to video" again. The engine reloads from the browser's cache and the files are checked again. On a phone a large video can take minutes, so cut it down first in the Video Trimmer or Video Compressor.

It says "“song.mp4” has no sound in it. Choose a song or another audio file."

The tool reads each file's streams as soon as it lands. The music box accepts a video, but a video with no sound track, such as a silent screen recording, has nothing to use, and the main button stays greyed out. Choose a file that has sound. The video box has the matching message, "“voice.mp3” has no video picture in it. Choose a video file.", for a file with no picture, such as an audio file.

It says "The finished video would be about 2.1 GB, more than a browser can build in one go. Compress or trim the video first, then add the music."

For a copied picture the estimate is the video's size plus the new sound. A re-encode is estimated from frame size and length. A browser's in-memory output file stops at about 2 GiB, so the button is held above 1.75 GB. Use the "Compress" or "Trim" shortcut under the message, then add the music. The softer "The finished video will be about 1.2 GB. That is a lot for a browser…" is only a warning.

It says "holiday.mov could not be read. If it is stored in Google Photos, iCloud or a cloud drive, save it to this device first, then choose it again."

The drop zone reads each file the moment you pick it. A phone copies picked files of up to 64 MB in total into memory then; larger files get a one-byte test read. The usual cause is a cloud-only file that was never fully downloaded. Save it to the device and pick it from there. If a file goes missing after it was accepted, the run shows "This file changed or moved after you picked it — please choose it again." and that box is emptied.

It says "The video ends before that. Choose an earlier start for the music."

"Music starts at" is at or past the end of the video, so there is under 0.05 seconds of room for the music, and the main button is greyed out. Type a smaller number. Its twin, "The song is shorter than that. Choose an earlier point to start it from.", means "Start the song from" is at or past the end of the song. Both messages need the lengths, which the tool reads from the files, so they appear once the files have been checked.

How it compares

This tool puts one song, or the sound of one video, under one video. You choose where it starts, its volume, whether it repeats, and the fades, and it saves an MP4, or a WebM for VP8 and VP9 sources. When the picture's codec allows it, the picture is copied unchanged and only the sound is encoded. It does not cut the video, pick a middle section of the song, layer several songs, change volume over time or choose a different sound track of the video. A video editor on your computer does those, and suits long or very large videos better. In exchange nothing needs installing, and the files stay in your browser.