Files stay private
Processing runs on your device. No media upload or server processing queue.
Merge Video and Audio Online
Add or replace audio in a video online. The selected audio becomes the new soundtrack; this tool does not mix it with the original sound.
01
Your video
▸Drop a video here
MP4 · MOV · WebM · MKV · AVIThis browser cannot preview the file. You can still try merging it locally.
02
Your audio
♪Drop an audio file here
MP3 · M4A · AAC · WAV · FLAC · OGGThis browser cannot preview the file. You can still try merging it locally.
Up to 2 GB combined · one video + one audio file
Loading the local merge engine
0%
✓Merged on your device
Your video and audio, together
Browser previews depend on the output format and codecs. If playback is unavailable or silent, download the file and check it in a compatible player.
File size—
Format—
Quality—
!
Unable to merge these files
Selected files—
MP4 output · original video and audio quality · both tracks kept in full
♪
The selected audio replaces the video’s original sound. This tool does not mix the two soundtracks.
▣Your files stay on your device. Audio and video are processed in this browser, never uploaded.
Only use music, voiceovers, and videos you own or have permission to use.
↓
You can also merge video and audio with the free AirMore Video Helper. Download for free
Add audio to video without uploading your files
Pair a silent clip with music, add a finished voiceover, or replace audio in a video. Choose one video and one audio file; the new soundtrack replaces the original sound rather than mixing with it.
Video track
+ Audio track
→ Merge locally
→ One download
Compatible video and audio tracks are copied into an MP4 without re-encoding, preserving the original video resolution and frame rate. Best for prepared tracks: this tool does not trim, loop, auto-sync or adjust volume. Use media you own or have permission to edit.
- Best for
- Adding music to silent videos, replacing an old soundtrack, and combining separately recorded video and narration that you have aligned beforehand.
- Not supported
- Mixing audio tracks, fades, automatic synchronization, trimming, looping, volume balancing, and multitrack editing.
How to merge video and audio
- 1
Choose two files
Select your video and audio, or drop them into their separate areas.
- 2
Check your files
Use one video and one audio file, up to 2 GB combined. Both tracks start together and are kept in full; prepare their timing before merging.
- 3
Merge and download
Let your browser combine the tracks, then save the finished file.
Merge audio and video without re-encoding
Give your video its soundtrack
Keep your picture
The video is copied without re-encoding, preserving its resolution and encoded frames.
Ready to save
Download one MP4 containing your selected video and audio tracks.
Add music to a silent video
Pair your footage with music you own or are licensed to use. Existing video audio is replaced, not mixed.
Combine separate video and audio
Reunite matching tracks saved separately. Align their starting points beforehand; there is no automatic synchronization.
Add a voiceover to video
Attach a prepared narration track to an explainer or screen recording without re-encoding the picture.
Frequently Asked Questions
Can I add audio to video online without uploading?
Yes. This free video and audio merger reads and combines files on your device, without an account. Your browser downloads the processing engine, but your media is not sent to a processing server.
Can I merge video and audio without losing quality?
Yes, when the source codecs are compatible. The video and selected audio tracks are copied without re-encoding. This preserves the encoded picture; it does not enhance resolution or repair an existing recording.
Can I add background music while keeping the original sound?
No. The selected audio replaces the original soundtrack; the tool does not mix music with existing speech. It uses the first audio track in your selected file and excludes original audio, subtitles and extra tracks. Use a multitrack editor if you need mixing, fades or volume balancing.
What happens if the audio and video have different lengths?
Both tracks start at the beginning and remain complete. Shorter audio leaves the remaining video silent. If the video is shorter, audio can continue after the picture ends; playback and the final picture depend on the player. This tool does not automatically loop, trim or pad either track. If you need both tracks to end together, trim and align your files in another editor before merging.
Can I combine MP3 and MP4, and why might merging fail?
You can select an MP4 video and MP3 audio, but the codecs must be supported by the MP4 container and local engine. A supported extension alone does not guarantee compatibility. Convert incompatible files separately; if the result will not preview, check it in a compatible media player.
Can I use this on a phone?
A browser with WebAssembly and Web Workers can run the tool. Large files can exceed a phone’s memory, so smaller files are more suitable.