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Free AV Muxer

Add Audio to Video (Muxing)

Combine separate video and audio files into a single high-quality container. Replace original sound or add a new soundtrack.

System Architecture
Zero-Exposure Pipeline

Media data remains local within the browser's volatile sandbox. FFmpeg is executed as a WebAssembly binary. No egress of raw bits occurs.

Core Compute Nodes

Single-threaded processing by default for max stability. Multi-threading enabled via SharedArrayBuffer where environment supports.

Shared by 85,000+ Developers

API CONTROL
Cluster: Lambda.6

Perfect Synchronization

Have a video file and a separate high-quality audio recording? Our muxing tool lets you marry them perfectly into a single MP4 or MKV file without quality loss.

Replace Audio

Swap out the original camera audio with a clean studio recording.

No Re-encoding

Use copy stream mode to merge files instantly without quality loss.

Format Support

Combine MP4 video with MP3, WAV, or AAC audio seamlessly.

How to Mux Audio/Video

1

Upload Files

Upload your video file and your audio file separately.

2

Sync

Adjust the start time if needed.

3

Mux

Combine them and download the final file.

Frequently Asked Questions

Will the video quality degrade?

No, if you choose 'Copy Stream', the video is untouched, preserving 100% quality.