Will adding music reduce my video quality?

No. In both Replace and Mix modes, Zolkit copies the video stream without re-encoding. Only the audio is processed. Your video track is preserved at exactly the original quality.

What if my music is shorter than the video?

In Replace mode, the output is trimmed to the length of the shorter file (usually the music). If you want the music to loop, you'll need to pre-extend it in an audio editor. In Mix mode, the output also ends at the shorter file. To fill the full video length, use a music track that is as long as or longer than the video.

Can I adjust the volume of the added music?

Volume control is not currently available in Zolkit's tool. For precise volume mixing, use a dedicated audio editor to adjust the music volume before uploading it here. Audacity is a free, open-source option for volume adjustment.

What video and audio formats are supported?

Video: MP4, MOV, AVI, MKV, WebM, WMV, and most other common formats. Audio: MP3, AAC, WAV, FLAC, OGG, M4A. The output is always MP4.

Add Music to Video Online

Add music or audio to any video online. Replace or mix audio tracks in MP4, MOV, AVI videos in your browser — no upload, no account, free.

Drop your video here

or click to browse

MP4, MOV, AVI, MKV, WebM, WMV supported

Drop audio file here

or click to browse

MP3, AAC, WAV, FLAC, OGG, M4A supported

Audio Mode

Adding background music to a video is one of the most common video editing tasks for social media content, presentations, and personal projects. Zolkit's 'Add Audio to Video' feature lets you merge any audio file (MP3, AAC, WAV, FLAC, OGG) with any video file entirely in the browser. Replace mode removes the original audio and substitutes your music track — ideal for silent screen recordings, timelapses, or videos where you want full music without background noise. Mix mode blends the original audio (speech, ambient sound) with the new music at equal volume — useful for adding subtle background music to a talk or podcast video. In both modes, the video stream is copied without re-encoding, which means the processing is extremely fast (typically 2–5 seconds for any file size) and the video quality is preserved exactly. The output ends at the shorter of the two files — if your music is shorter than the video, the video is trimmed to match.

Related Use Cases

← Video Joiner Merge Phone Video Clips Combine Video Clips Online

Free Online Video Joiner — Merge Video Clips in Your Browser

Zolkit's Video Joiner uses FFmpeg WebAssembly to combine video clips and merge audio with video entirely in your browser. Upload multiple MP4, MOV, AVI, MKV, or WebM files, arrange them in order, and join them into a single MP4 — without uploading a single byte to a server. Quick Join copies streams without re-encoding for near-instant results with same-format clips. Smart Join re-encodes with H.264 to handle clips from different cameras, resolutions, and codecs. The Add Audio tab lets you replace or mix an audio track into any video file. All processing runs locally on your device.

100% Private

Your videos never leave your device. All processing runs in WebAssembly inside the browser tab — no server, no cloud, no data retention.

Join Any Clips

Quick Join copies streams for near-instant merging of same-format clips. Smart Join re-encodes with H.264 to handle clips from different devices and resolutions.

Drag to Reorder

Arrange clips in any order by dragging. See filenames and sizes at a glance. Remove any clip before processing.

Add Audio to Video

Replace a video's audio track with music or a voiceover, or mix the new audio with the original. Supports MP3, AAC, WAV, FLAC, and OGG.

FFmpeg-Powered

Uses FFmpeg's concat demuxer for copy mode and filter_complex concat for re-encode mode — the industry standard for video joining.

Free, No Account

No subscription, no sign-up, no watermark, no file count limit. Zolkit's Video Joiner is completely free.

How to Merge Video Clips Online

1
Click 'Join Videos' tab, then drop your video files onto the upload zone or click to select multiple files. Files are listed in join order.
2
Drag clips to reorder them. Choose Quick Join (for clips from the same device/camera) or Smart Join (for clips from different sources). Set quality and resolution if using Smart Join.
3
Click 'Join Videos', wait for processing, then download the merged MP4. For adding audio, switch to the 'Add Audio to Video' tab and upload one video plus one audio file.