What you should know
- MP4 is the most compatible output for phones, browsers, and editing tools.
- WebM can be smaller, but VP9 encoding is slower and not every player supports it.
- Very large or long files may exceed browser memory. The tool warns above 250 MB and refuses above 1.5 GB.
- Codec support depends on the pinned FFmpeg build. A failed combination is reported, never silently replaced.
Privacy of local processing
Your file is read with the browser File API and written into FFmpeg's in-memory filesystem inside this tab. The only third-party request is the pinned FFmpeg core from jsDelivr, loaded the first time you run a job. Your file bytes are never sent to Fetchora or jsDelivr. Closing or reloading the tab clears the in-memory filesystem.