About M4A and AIFF

M4A is AAC audio in an MP4 container — the default format of the Apple ecosystem and most streaming services. AAC compresses more efficiently than MP3, so the same bitrate sounds a little better.

AIFF is Apple's uncompressed audio format — the same raw PCM as WAV in a different wrapper, dating back to 1988. It's still the native interchange format for Logic Pro and much of the mac production world, and converts to WAV with zero quality change.

Converting M4A to AIFF produces a lossless file, though detail already discarded by M4A's compression can't be recovered — the new file is a faithful copy of the M4A, not of the original recording.

How the conversion works

This tool runs FFmpeg — the same engine behind most media software — compiled to WebAssembly, entirely in your browser. Your file is read locally, converted locally, and saved straight from memory; nothing is ever uploaded, which also means no queues and no server-side file size limits.

The converter itself is a one-time ~31 MB download on your first conversion, cached by the browser afterwards. Once it's loaded, everything works offline.