Add Audio to Video
Add music, replace a soundtrack, or mix narration over a video — no re-encode of the picture.
- With a video: mix keeps the original sound underneath; replace swaps it entirely.
- With two audio files: both are mixed into one MP3 (the second file uses the volume slider).
Why add background music, voice narration, or sound effects to video?
Layering music beds over screen recordings, replacing noisy original video audio, or adding voiceover narration is a fundamental video editing task:
- Replace Noisy Original Video Audio (Replace Mode): Strip unwanted camera noise or background chatter and replace it with a clean music track or voiceover.
- Mix Background Music Under Speech (Mix Mode): Layer gentle background music (at 30-50% volume) under existing dialogue or voice narration.
- Lossless Video Stream Copying (Zero Re-Encoding): Copies video frames bit-for-bit (`-c:v copy`), preserving 100% original visual quality and finishing in seconds.
- 100% Private On-Device Execution: Combine private family videos and confidential business clips locally without uploading to cloud servers.
FFmpeg WebAssembly video stream copy & amix engine
ToolJiffy uses a high-performance client-side FFmpeg WebAssembly pipeline:
The engine stream-copies video packets (`-c:v copy`) while applying FFmpeg’s amix audio filter to blend audio streams at specified volume ratios, re-encoding audio to 192 kbps AAC inside an MP4 container.
Client-side security for private media files
Uploading private family videos, corporate presentation recordings, or unreleased content to third-party cloud video tools creates severe privacy risks.
ToolJiffy operates on a zero-cloud architecture. By leveraging client-side WebAssembly, adding audio runs 100% locally in your browser memory. Your video files never touch external cloud servers.
Step-by-step guide to adding audio to video
- Upload video & audio: Select one video file and one audio file in the box above.
- Choose mode & volume: Select Replace or Mix, and set added audio volume (10-200%).
- Process & Download: Click Add Audio to process and save your updated MP4 file.
Explore related video & audio editing utilities
To extract audio from video clips, use Extract Audio, trim audio clips with Trim Audio, mute original video sound using Mute Video, or compress files with Video Compressor.
Frequently Asked Questions
How do I add background music or audio to a video online for free without uploading?
Upload one video file and one audio file above, choose Replace mode (swapping sound) or Mix mode (layering background music over original audio), set added audio volume, and click Add Audio. ToolJiffy combines them in browser memory.Does adding audio to video re-encode or degrade video visual quality?
No! ToolJiffy uses stream copying (`-c:v copy`) for video frames. The video picture is copied bit-for-bit without re-encoding, preserving 100% original visual quality and rendering in seconds.What is the difference between Replace Audio mode and Mix Audio mode?
Replace mode removes the original video audio track entirely and replaces it with your new audio file. Mix mode keeps the original video audio and layers your new audio track underneath with volume slider control (10% to 200%).Is my video or audio file uploaded to any cloud server?
No, 100% private. Video demuxing, audio mixing, and AAC audio encoding take place locally inside your browser memory using FFmpeg WebAssembly. Your files never touch external cloud servers.What happens if the added audio file is longer or shorter than the video clip?
In Replace mode, output video length matches video duration. In Mix mode, original video duration is maintained.What video and audio file formats are supported?
ToolJiffy accepts MP4, MOV, WebM, AVI, and MKV video files, alongside MP3, WAV, M4A, and AAC audio files.Can I mix two audio files together without a video?
Yes! Drop two audio files into the tool, and ToolJiffy will mix them into a single downloadable MP3 file.Is ToolJiffy Add Audio to Video free to use without limits or watermarks?
Yes! ToolJiffy is 100% free with unlimited usages, zero account sign-ups, and zero watermarks.