FLAC stands for ‘Free Lossless Audio Codec’ and can shrink a file to roughly 50-60% of its original size; when decompressed, the file goes back to its original state.
Considering that there is no loss of quality because of this compression, the format is extremely popular. Microsoft executive Joe Belfiore has now revealed that Windows 10 for phones and tablets will also natively support this file format.
@Lisan_09 Yes, FLAC support will be on phones/small tablets… won’t be in the first insider build, though, will be a few months later..
— joebelfiore (@joebelfiore) January 28, 2015
However, native FLAC support will not be available in the first insider build; which is slated for a February release, but will come a few months later according to Belfiore.