This runs in your browser. Nothing is uploaded. Longer clips take longer here than they would on a fast server — that is the trade-off for not sending the file.
About Stereo to mono
Downmixes a recording to one channel in the browser with FFmpeg. Nothing is uploaded.
Two channels become one. Useful for voice that was recorded stereo by accident, or a file a CMS insists is mono. Music will collapse the stereo image. That is the point of the tool, and also the warning. It mixes both sides; it does not keep left and trash right.
Stereo to mono runs FFmpeg compiled to WebAssembly in this tab. The first visit of a video or audio tool fetches about 30 MB from this origin; after that it can stay cached. Your file is not in that download and is not POSTed anywhere. GPL FFmpeg, single-thread, same origin, no COEP experiment. That is the same encoder as convert, trim, and compress — this page is just a different argument list, with the same honesty about what the core cannot mux.
You can open the network panel and watch. Encoding a long clip on a phone is slow because it is your CPU. That wait is the trade for not handing the file to a converter you found in a search ad. Reverse and boomerang cap duration so a two-hour file does not try to live backwards in RAM. If a codec inside a familiar extension is missing from this core, you get an error rather than a silent broken file. Subtitle generation and stem splitting are not here; I will not pretend they are. Missing is better than a watermarked demo.
How to use Stereo to mono
- 1Drop audio.
- 2Click Downmix, then download.
What it won't do
- Always MP3 out.
- No “keep left only” option.
Common questions
Does stereo-to-mono upload the file?
No.
Is this the same as dropping one channel?
It is a mix to one channel, not “keep left, trash right.” Both sides are combined.
Will a mono file get smaller?
Usually, at the same bitrate, because there is one channel to encode. Output is still MP3.
Related tools
Why this one doesn't upload your file
There is no server to upload to. This page is a static file, and the work happens in your browser using the same graphics and WebAssembly code that renders every other site you visit. Your file is read from disk into memory, processed, and handed back as a download. Once the page has loaded you can disconnect from the network entirely and it keeps working. The longer explanation