Video Editor
Add multiple sound effects to a video directly in your browser. No upload, no server processing, and no complicated timeline editor.
Browser-based FFmpeg WASM processing • Best for reels, shorts, clips and videos under a few minutes
SFX mixer
Add start time, volume, fade in and fade out for each sound.
The SFX preview slider is linked with Volume %. Browser preview is capped at 100%; export volume can still be set higher from the Volume % box.
Video Editor Online
Add multiple sound effects to videos online without using a complex desktop editor. Upload a video, add SFX files, set exact start times, adjust volume, add fades, and export a final MP4 directly from your browser.
How to add sound effects to a video
Upload video
Choose the MP4 or video file you want to edit.
Add sound effects
Upload one or more SFX audio files such as MP3, WAV, M4A, AAC, OGG, or FLAC.
Set SFX timing
Enter the start time in seconds for each sound effect and adjust its volume.
Add fades if needed
Use fade in and fade out values to make sound effects smoother.
Export video
Click Export Video and download the final MP4 with all sound effects mixed in.
Use this tool when you already have a voiceover or background music and only need to place extra sound effects such as cinematic booms, whooshes, hits, risers, transitions, heartbeats, ambience, or notification sounds at exact moments.
For best results, keep SFX volume lower than the voiceover. Start around 60% to 80%, then reduce loud impacts if they overpower speech.
Video SFX mixer
Add many SFX files in one export instead of uploading and exporting again and again in simple online editors.
Made for reels and shorts
Ideal for YouTube Shorts, Instagram Reels, TikTok videos, educational clips, mystery videos, storytelling videos, and product demos.
Private browser processing
The editor uses browser-based processing, so your video can be mixed locally without server upload for normal short clips.
Best use cases
- Add cinematic booms to mystery and space videos.
- Add whooshes, hits, risers, and transition sounds.
- Place heartbeats, ambient sweeps, and notification sounds.
- Improve YouTube Shorts and Instagram Reels without a full editor.
- Mix sound effects into voiceover videos.
- Create one final MP4 with all SFX in a single export.
Important note
This editor uses FFmpeg WebAssembly in your browser. The first load can be larger than normal tools because the video engine must be loaded. After caching, future loads can be faster.
Browser video processing uses memory. Use short MP4 clips for best results. Very large videos may be slow or may fail on mobile or low-memory devices.
Video Editor FAQ
Is this video editor free to use?
Yes. SmartTools Video Editor is free to use online for adding sound effects to videos.
Does the video upload to a server?
No. This tool is designed for browser-based processing using FFmpeg WASM, so your video can be processed locally in your browser.
Can I add multiple sound effects at once?
Yes. You can upload multiple SFX files, set a start time for each one, adjust volume, and export one final MP4 video.
Which video format works best?
MP4 works best for browser processing and final export. Short reels, shorts, clips, and social media videos are ideal.
Can I keep the original voiceover or background music?
Yes. Keep original video audio enabled if your video already has voiceover or background music and you only want to add extra SFX.
Why is the first load slower?
The tool loads FFmpeg WebAssembly in the browser. After the first load, browser caching can make future visits faster.
Will this work on mobile?
It may work for small videos, but desktop browsers are recommended because browser video processing can use significant memory.
Will my original video change?
No. The original video remains unchanged. The tool creates a new MP4 file for download.
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