Why this tool is useful
Layer commentary, background music or an effect over a private clip while controlling the original and added track levels separately.
Local File Tools · runs locally
Private Audio and Video Mixer
Mix one short browser-decodable video's existing soundtrack with one selected audio file and export WebM without uploading either source.
Ready. Your working data stays in this browser.
Files and capture streams stay on this device. Processing uses browser APIs only; nothing is uploaded to YTSave, the media API or a proxy.
How it works
Web Audio decodes both tracks, applies bounded gain values and feeds their mix into the same local MediaRecorder timeline as the browser-rendered video frames.
Practical example
Keep interview audio at 100%, add quiet music at 25%, then verify the reported mix levels and local-only processing before download.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.