FLAC-HD is a high resolution audio format for audiophiles to enjoy more than three times the fidelity of a standard audio CD. Typically LiveMetallica FLAC-HD files are recorded at 24 bit / 48 KHz for maximum fidelity. Follow the instructions in this FAQ for standard FLAC playback to listen to FLAC-HD files.  For more information on 24 bit audio, please see these Wiki pages on High-Resolution Audio and Audio bit depth.