Audio Converter
Convert audio between MP3, AAC, FLAC, WAV, Opus and more, entirely in your browser. Nothing is uploaded.
Online converters work by uploading your file to someone else's server, converting it there and sending it back. That's slow for big files, and it means handing your recordings to a stranger. This one runs FFmpeg compiled to WebAssembly inside the page, so the conversion happens on your own machine and your files never leave it.
What it does
- Formats: MP3, M4A/AAC, raw AAC, OGG Vorbis, Opus, FLAC, ALAC, WAV, AIFF, WMA and AC3 out; anything FFmpeg can read in, including the audio track of video files.
- Options: bitrate or quality, channels, sample rate, loudness normalization (EBU R128) or a fixed gain, and trimming.
- Batches: drop in a stack of files, convert them all with the same settings, and download them one by one or as a zip.
How it works
The page loads ffmpeg.wasm into a Web Worker. Input files
are mounted into its virtual filesystem straight from disk rather than copied into memory, then a
normal ffmpeg command line runs against them. The output is handed back to the page as a download.
The FFmpeg build is about 31 MB of WebAssembly. It's stored Brotli-compressed, so the first visit downloads about 7 MB, and later visits revalidate it from the browser cache.
Limits
- Everything runs in one browser tab, so very large files (several GB) can run out of memory.
- Opus uses FFmpeg's built-in encoder, because libopus crashes in the current ffmpeg.wasm build. It's good at normal bitrates but weaker than libopus at very low ones.
The source is in apps/audio-converter.