What Is the FLAC Audio Format?

FLAC definition

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The Free Lossless Audio Codec is a compression standard originally developed by the nonprofit Xiph.org Foundation that supports digital audio files that are acoustically identical to the original source material. FLAC-encoded files, which usually carry the .flac extension, are notable for having a fully open-source construction as well as small file sizes and swift decoding times.

FLAC files are popular in the lossless audio space. In digital audio, a lossless codec is one that does not lose any important signal information about the original analog music during the file-compression process. Many popular codecs use lossy compression algorithms—for example, the MP3 and Windows Media Audio standards—which lose some audio fidelity during rendering.

Ripping Music CDs

In fact, many users wishing to back up their original audio CDs (​CD ripping) opt to use FLAC to preserve the sound rather than using a ​lossy format. Doing this ensures that if the original source is damaged or lost, then a perfect copy can be reproduced using the previously encoded FLAC files.

Out of all the lossless audio formats available, FLAC is perhaps the most popular one in use today. In fact, some HD music services now offer tracks in this format for download.

Ripping an audio CD to FLAC typically produces files with a compression ratio of between 30 percent and 50 percent. Because of the format's lossless nature, some people also prefer to store their digital music library as FLAC files on external storage media and convert to lossy formats (MP3, AAC, WMA, etc.) when needed—for example, to sync to an MP3 player or another type of portable device.

FLAC Attributes

The FLAC standard is supported on all major operating systems, including Windows 10, macOS High Sierra and above, most Linux distributions, Android 3.1 and newer, and iOS 11 and newer.

FLAC files support metadata tagging, album cover art, and fast seeking of content. Because it's a nonproprietary format with royalty-free licensing of its core technology, FLAC is especially popular with open-source developers. In particular, FLAC's fast streaming and decoding compared to other formats make it suitable for online playback.

From a technical perspective, the FLAC encoder supports:

  • Sampling rates between 1 Hz to 65,545 Hz in 1 Hz steps, or 10 Hz to 655,350 Hz in 10 Hz steps, using between one and eight channels
  • PCM bit resolution of 4 to 24 bits per sample (although only fixed-point, and not floating-point, samples are supported)

FLAC Limitations

The chief drawback to FLAC files is that most hardware doesn't natively support it. Although computer and smartphone operating systems have started supporting FLAC, Apple didn't support it until 2017 and Microsoft until 2016—despite the fact that the codec was first released in 2001. Consumer hardware players generally do not support FLAC, instead relying on lossy-but-common formats like MP3 or WMA.

One reason FLAC may have had slower industry adoption, despite its superiority as a compression algorithm, is that it does not support any sort of digital-rights management capability. FLAC files are, by design, not encumbered by software licensing schemes, which has limited its usefulness for commercial streaming vendors and the commercial music industry as a whole.