Reference
What is ALAC?
ALAC (Apple Lossless Audio Codec) is a lossless codec developed by Apple. It reduces PCM file size without changing the decoded sample values.
ALAC technical data
| Property | Codec capability |
|---|---|
| Bit depths | 16, 20, 24 and 32-bit integer PCM |
| Sample rate | Arbitrary integer rates through 384 kHz are explicitly supported by Apple's published codec code/documentation |
| Channels | 1–8 |
| Compression | Lossless |
| Typical container | MP4/M4A or CAF |
ALAC is not the same thing as M4A
ALAC is the codec. .m4a normally identifies an MP4-family audio file and can contain ALAC or AAC. Two M4A files can therefore use completely different compression.
ALAC vs FLAC
Both are lossless codecs: decoded audio can be bit-for-bit identical to the input PCM. The practical difference is ecosystem and container support rather than sound quality. See FLAC vs ALAC.