A few manufacturers, notably Sony and Panasonic, have implemented wireless connection technology for the surround speakers in this class of equipment. This technology may be available as standard with some of the high-priced models or may be supplied as an aftermarket kit that only works with selected models in the manufacturer's range. It usually uses a line-level feed over a proprietary wireless link to a separate power amplifier used for the surround-sound channels. This link-receiver and power amplifier can be built into one of the surround speakers or housed in a black box that the surround speakers are connected to. Some higher-end HTIB models offer additional features such as 1080i or 4K ( mainly versions with Blu-ray) video resolution upscaling, a 5-disc platter, HDMI inputs, USB connectivity, Bluetooth support, Wi-fi support, Internet apps, DAB and DAB+, mirroring possibility, iPod dock and a hard disk for recording TV shows.