About M4A and FLAC

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.

FLAC is lossless compression for audio — bit-identical to the source at roughly half the size of WAV. It's the archival format of choice for music collections and masters.

Converting M4A to FLAC 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.