FLAC is a lossless audio format that compress audio files without loss in quality. By default Windows Media Player does not support FLAC formats. To play FLAC files in WMP, you need to install the codecs.

You can download and install either Illiminable or CoreFLAC DirectShow filters. Illiminable codec installs both Ogg Vorbis and FLAC filters. After installing the codec, you should be able to play FLAC files indrectly in WMP.