The aptX audio codec is a proprietary audio codec compression algorithm, which allows the real-time streaming of high quality stereo audio over a Bluetooth A2DP connection between a source device and the accessory device.

aptX technology must be incorporated in both the source and the accessory device for it to have any effect. Full backwards compatibility however allows audio streaming even when one of the devices is not aptX compatible, though in this case, the connection won't benefit from the technology.