Which functionality must a head unit support for Bluetooth streaming audio from a smartphone?

To enable Bluetooth streaming audio from a smartphone, a head unit must support the Advanced Audio Distribution Profile (A2DP). This profile is specifically designed for streaming high-quality audio over a Bluetooth connection, allowing the head unit to receive and play audio from a compatible smartphone or other Bluetooth-enabled devices. A2DP facilitates the transmission of stereo audio, which is essential for enriching the listening experience in mobile audio systems.

Other profiles, while important for different functionalities, do not provide the capability to stream audio directly. AVRCP (Audio/Video Remote Control Profile) is primarily used for remote control commands, like play and pause, rather than actual audio transmission. HSP (Headset Profile) and HFP (Hands-Free Profile) primarily serve communication functions, allowing for voice calls through a Bluetooth headset or car system but do not support audio streaming in the same way that A2DP does. Therefore, the presence of A2DP support in a head unit is critical for Bluetooth audio streaming from a smartphone.