It looks like you’ll be able to play FLAC audio files in the next version of iOS. According to The Next Web, developers who have gotten a hold of the iOS 11 beta early are reporting that there is now full playback support for the high-quality files, which means you’ll be able to play them from an iPhone and iPad. The functionality is apparently part of the new Files management system. As of right now, FLAC files aren’t compatible with the current version of iTunes, but presumably that will change closer to the release of iOS 11, which is due out in the fall.