Earphones (Frequency response): 20Hz to 20, 000Hz. Impedance: 32 ohms. Dimensions: 1.5""W x 3.6""H x .24""D. Weight: 1.28oz.. Battery and power . Built-in rechargeable lithium-ion battery. Playback time. Music playback time: Up to 24 hours when fully charged. Video playback time: Up to 5 hours when fully charged. Charging via USB to computer system or power adapter (sold separately). Fast-charge time: about 1.5 hours (charges up to 80% of battery capacity). Full-charge time: about 3 hours. Mac system requirements . Mac computer with USB 2.0 port. Mac OS X v10.4.11 or later. iTunes 9 or later. iPhoto 6.0.6 or later recommended for use with Mac OS X Tiger. iPhoto '09 recommended for use with Mac OS X Leopard or Snow Leopard. Windows system requirements . PC with USB 2.0 port. Windows Vista or Windows XP Home or Professional with Service Pack 3 or later. iTunes 9 or later. Environmental requirements . Operat