Volume
Controls only the added track before the final mix. Lower it beneath dialogue; 100% means the source level of that audio file, not a universal loudness target.
Add Audio to Video
Add background music, voice-over or a sound effect to a video. Control volume, timing, fades, looping and the source soundtrack before exporting a new MP4.
Mix or replace audioPrecise time rangeBrowser-based workflow
Read the full guide1. Select video
Drop a video here
or click to browse
Supported formats: MP4, WebM, MOV, MKV
Maximum file size: 2 GB
2. Add audio
Drop an audio file here
or click to browse
Supported audio: MP3, WAV, M4A, AAC, OGG, FLAC
Maximum audio size: 500 MB
3. Audio settings
70%
Loudness of the added track in the final mix.
1.0 s
1.0 s
When the added audio begins on the video timeline.
When the added audio stops on the video timeline.
Turn off to silence the video soundtrack.
Scale the mixed signal so its highest peak stays below clipping.
Repeat the added track until the selected range is filled.
Preview
Select a video and an audio file to preview the mix.
No videos have been added yet.
Result
Result
Download the result before closing or refreshing this page.
- Original size
- -
- Output size
- -
- Saved
- -
- Resolution
- -
- Duration
- -
- Format
- MP4
- Audio
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When confirmed by the source, local video and audio files are decoded, mixed and encoded in the browser. URL mode still requests each file from its host, so CORS, authentication, expiry and range behavior can block processing.
How do I add background music without removing the original audio?
Choose Background as the track position, keep original audio enabled, lower the added track to a level that does not cover speech, and use fades for a smoother entrance and ending.
Choose whether the new track mixes with or replaces the original
Background mode plays both tracks together. Replace mode removes the source soundtrack. Voice-over mode keeps the source quieter under narration. The exact ducking level must match the implementation rather than a marketing claim.
Who is this for?
Creators can add music to social clips, teachers can add narration to lessons, product teams can score demos, podcasters can prepare promo videos, and support teams can annotate screen recordings with a voice track.
Practical uses
- Add background music to a product or social video.
- Record narration separately and place it over a screen capture.
- Replace noisy camera audio with a clean track.
- Add a short sound effect at a specific time.
- Loop an ambience bed through a longer clip.
How to add audio to a video
Choose a video, then add an audio file from the device or a direct public URL.
Select Background, Replace or Voice-over based on what should happen to the source soundtrack.
Set volume, start time and end time; add fade-in and fade-out when abrupt edges would be distracting.
Use Loop only when a shorter track should repeat, and Normalize only after reviewing the intended balance.
Preview the mix, process the files and check speech clarity, clipping, sync and the final duration before delivery.
Understanding the audio controls
Fade in and fade out
Fades smooth the beginning and ending of the added track. They must fit inside the selected playback window.
Start and end time
These values place the added track on the video timeline. Outside that window, the added track is silent.
Background, Replace and Voice-over
Background mixes both tracks, Replace removes the original soundtrack, and Voice-over reduces the original so narration stays prominent.
Normalize and Loop
Normalize prevents peak clipping by scaling the final mix; it does not master perceived loudness. Loop repeats a short audio file to fill the selected range.
How the files are handled
When confirmed by the source, local video and audio files are decoded, mixed and encoded in the browser. URL mode still requests each file from its host, so CORS, authentication, expiry and range behavior can block processing.
Audio mixing limitations
- Mixing cannot remove background noise or separate voices from an existing track.
- Normalization based on peaks does not guarantee equal perceived loudness across all content.
- Very long or high-resolution video can exceed browser memory during re-encoding.
- Supported audio and video codecs depend on the current browser and engine.
Common mixing problems
Narration is hard to hear
Lower the original soundtrack, choose Voice-over mode, or reduce the added music. Preview on speakers and headphones.
The mix sounds distorted
Reduce volume levels or enable normalization. If the source already clips, normalization cannot restore damaged samples.
The added track stops too early
Enable Loop when repetition is acceptable, or provide a longer audio file and check the end time.
Audio is out of sync
Verify the start time, source duration and browser decode support. Variable frame rate or unusual timestamps can also affect some pipelines.
Add audio to video FAQ
Can I keep the original audio?
Yes. Choose Background and leave Keep original audio enabled. Lower the added track so speech remains understandable.
What is the difference between Background, Replace and Voice-over?
Background mixes both tracks, Replace uses only the new track, and Voice-over lowers the source beneath narration.
What does audio ducking do?
Ducking temporarily or continuously lowers the source soundtrack so voice-over is easier to hear. The actual reduction should be described from the implementation.
Can a short music track repeat?
Yes when Loop audio if shorter is enabled. The track repeats until the selected end time or the video ends.
Does Normalize audio improve quality?
It reduces the risk of peak clipping by scaling the final mix. It does not remove noise, repair distortion or guarantee broadcast loudness.
Can I add audio without uploading my files?
Yes when local processing is implemented in the browser. URL sources still come from remote hosts.
Will the original video be changed?
No. The tool should export a separate video with the new mix.
Why is the output larger?
The video is typically re-encoded and now contains a new audio stream. Size depends on video settings, audio bitrate, duration and codec.