Audio & video / Local FFmpeg tool
Re-encode audio as MP3 at a specific constant target bitrate.
The first run loads an approximately 31 MB FFmpeg WebAssembly core from this site. It does not use a CDN or upload your files.
Files are limited to 200 MB total and 20 minutes; mobile devices use an 80 MB limit. Reverse, GIF and boomerang tools have lower duration caps.
At most 60 download files are generated.
Validated downloads will appear here after processing.
Method, example & boundaries
Re-encode a supported audio file as MP3 at a chosen constant bitrate while keeping processing in the browser. Use it to make a deliberate size-versus-quality tradeoff for a real delivery channel, not to assign a larger number to an already degraded source.
An MP3 whose encoded audio payload is approximately 9.6 MB before container overhead: 128,000 bits × 600 seconds ÷ 8.The estimate is useful for delivery planning, while the downloaded file remains the authority because metadata and encoder framing add a small overhead.
FFmpeg.wasm decodes the selected source and encodes MP3 with LAME at the selected -b:a value. The process runs in a worker, preserves source duration, probes the output, and then exposes a local object URL for download.
Local AI / Speech to text
Open-source Whisper Tiny runs in your browser. The file, audio and result are never uploaded.
Choose an audio or video file in the workbench above first.
◎ The model loads only from 321Kit; MiniMax is not called and no transcript history is stored.
How it works
Lower bitrates reduce size by discarding more audio information.
Lower bitrates reduce size by discarding more audio information. Processing uses single-thread FFmpeg.wasm. The page does not upload, store or inspect file content outside this device. Cancel, error and page close terminate the worker and revoke temporary object URLs.
Re-encoding cannot improve a low-quality source by choosing a higher number. Files are limited to 200 MB total and 20 minutes; mobile devices use an 80 MB limit. Reverse, GIF and boomerang tools have lower duration caps.
Anonymous feedback
Found a problem or an idea to make this tool better? Tell us. We review every report and start working on actionable improvements within 2 days, continuously improving reliability and usability.