Convert to FLAC is a BASH shell script, and was originally written for use under Linux. It should, however, run under any OS that supports BASH.

Convert to FLAC currently supports the following input formats:

• Apple Lossless (ALAC) - requires alac and mp4info (for metadata) binaries
• FLAC (eg., for transcoding to a different compression ratio)
• Meridian Lossless Packing (MLP) - commonly found on DVD-Audio and Blu-ray discs; requires ffmpeg
• Monkey's Audio (APE) - requires mac and apeinfo (for metadata) binaries
• Shorten - requires shorten binary
• True Audio (TTA) - requires ttaenc binary
• WAVE
• WavPack - requires wvunpack binary
• Windows Media Audio Lossless (WMA) - requires ffmpeg

You can find the script on LegRoom.net and GitHub.