How to Decode Apple Lossless ALAC Using FFmpeg

This article provides a straightforward guide on how to decode Apple Lossless Audio Codec (ALAC) files using FFmpeg. You will learn the exact command-line syntax to convert ALAC files (typically found in .m4a containers) into uncompressed or widely supported lossless formats like WAV or FLAC, ensuring a seamless audio transition without any quality loss.

Basic Decoding to WAV

FFmpeg includes a native ALAC decoder, meaning you do not need to install any external libraries to read these files. To decode an ALAC .m4a file into an uncompressed .wav file, use the following basic command:

ffmpeg -i input.m4a output.wav

In this command: * -i input.m4a specifies your source Apple Lossless file. * output.wav is the target filename. FFmpeg automatically detects the .wav extension and decodes the ALAC stream to uncompressed PCM audio.

Decoding to FLAC

If you want to keep the file size compressed while maintaining lossless quality and improving compatibility with non-Apple devices, you can decode ALAC directly to FLAC:

ffmpeg -i input.m4a -c:a flac output.flac

Controlling Bit Depth and Sample Rate

By default, FFmpeg will preserve the original sample rate and bit depth of the ALAC file. However, if you need to force a specific bit depth (for example, converting a 24-bit ALAC file to a 16-bit WAV file), you can define the audio sample format:

To decode to 16-bit PCM WAV:

ffmpeg -i input.m4a -c:a pcm_s16le output.wav

To decode to 24-bit PCM WAV:

ffmpeg -i input.m4a -c:a pcm_s24le output.wav

Batch Decoding Multiple Files

If you have an entire folder of ALAC .m4a files that you need to decode, you can automate the process using a simple command-line loop.

For macOS and Linux (Terminal):

for f in *.m4a; do ffmpeg -i "$f" "${f%.m4a}.wav"; done

For Windows (Command Prompt):

for %i in (*.m4a) do ffmpeg -i "%i" "%~ni.wav"

These loops will search for every .m4a file in the current directory and decode it into a corresponding .wav file with the same filename.