A2DP & AVRCP

Advanced Audio Distribution Profile (A2DP) is a core Bluetooth audio transmission specification, aimed at achieving high-quality audio one-way transmission from the audio source to the receiving device in mono, stereo, or multi-channel modes.

Audio/Video Remote Control Profile (AVRCP) is a core Bluetooth audio control specification, designed to establish remote control and status synchronization mechanisms between audio/video devices, ensuring interoperability in functionality and interaction processes among related Bluetooth devices.

In A2DP applications, two roles are defined:

1. Audio Source (A2DP Source): The device responsible for providing the audio data to be transmitted, serving as the sender of the audio stream.

2. Audio Sink (A2DP Sink): The device responsible for receiving and decoding the audio stream, acting as the receiver and player of the audio stream.

In AVRCP applications, two roles are defined:

1. Controller (AVRCP Controller): The device initiating remote control commands, acting as the active party in control operations.

2. Target (AVRCP Target): The device receiving and responding to control commands, acting as the passive party in control operations.

Advantages of A2DP/AVRCP

A2DP is the core profile for Bluetooth audio transmission. With its wide adaptability, ease of use, and technical specificity, it has become the mainstream solution for wireless audio transmission in the consumer electronics sector. Its key advantages are primarily reflected in audio experience, device compatibility, technical design, and practical application.

1. Flexible Codec Support, Balancing Audio Quality and Compatibility

The profile mandates support for basic SBC encoding to ensure interoperability among all A2DP devices, meeting everyday music playback needs. Additionally, the protocol reserves the capability for high-definition audio encoding expansion, supporting advanced codecs such as AAC, aptX, LDAC, and LHDC (requiring support from both transmitting and receiving devices), enabling higher sound quality performance.

2. Wide Compatibility, Universal Across Devices and Platforms, Reducing Development Adaptation Costs

As a universal standard established by the Bluetooth Special Interest Group (SIG), the A2DP profile offers wide compatibility across various scenarios, including consumer electronics, embedded devices, and automotive electronics. Devices do not need to develop exclusive communication protocols; they only need to integrate the A2DP profile stack to achieve seamless connectivity with terminals such as phones, effectively reducing development and adaptation costs.

3. No Physical Cable Constraints, Simplifying Device Design

Compared to traditional wired audio interfaces (such as 3.5mm, USB), A2DP eliminates cable constraints through wireless transmission. This not only allows devices to adopt a sleek design without interfaces (such as true wireless earbuds, portable speakers), reducing hardware complexity and cost (by minimizing interface circuits and cables), but also enhances user convenience and freedom in scenarios like exercising and in-car use.

AVRCP is the core profile for Bluetooth audio control, and with its comprehensive standardized control command set, bidirectional communication capabilities, and good compatibility, it has become the mainstream solution for remote control between Bluetooth devices. Its core advantages are as follows:

1. Standardized Command Set, Covering All Scenario Needs

The profile defines complete and standard control commands. Once the device is integrated, it can directly support various operations without the need for custom instructions, including:

Basic Control: Play/Pause, Previous/Next track, Volume adjustment, Fast forward/Rewind, Stop;

Advanced Control: Track switching, Playback mode switching (Sequential/Loop/Random), Mute control, etc.;

Status Feedback: Devices can return playback status (Play/Pause/Stop), volume level, track information (song name, artist, album, duration) in real-time, allowing controllers (such as headphones, car panels) to display synchronously, enhancing user experience.

2. Bidirectional Communication, Balancing "Control" and "Feedback"

The profile supports bidirectional data transmission between the controller and the controlled device, ensuring reliable delivery of control commands and real-time synchronization of device status. This effectively prevents issues such as "control non-response" or "status display out of sync", making it particularly suitable for embedded device applications that require high interaction reliability.

Application Scenarios of A2DP/AVRCP Technology

A2DP and AVRCP are complementary core protocols in Bluetooth audio technology. A2DP is responsible for the wireless transmission of high-quality audio streams, while AVRCP provides remote control functions for audio playback. Together, they work in tandem to meet the audio interaction needs across various fields such as consumer electronics, automotive systems, and smart homes. Specific application scenarios are as follows:

Personal Consumer Audio Devices

This is the most basic and widely applied scenario for A2DP/AVRCP, mainly serving personal wireless audio playback and convenient control:

1. Bluetooth Headphones: Wireless Bluetooth headphones receive stereo audio streams from a mobile phone or computer. Users can send commands such as play/pause, track skipping, and volume adjustment through physical buttons or touch modules on the headphones. The mobile phone acts as the controlled device for AVRCP, responding to operations and providing track information feedback.

2. Bluetooth Speakers: Home or portable Bluetooth speakers receive audio and video streams from the audio source. Users can control playback through buttons on the speaker panel or a paired remote control. Some smart speakers can also obtain and display track metadata from the audio source via the AVRCP profile.

In-Car Bluetooth Systems

The automotive environment is a key application area for A2DP/AVRCP technology, aiming to balance entertainment experience and operational safety during driving. The in-car Bluetooth module receives audio streams such as music and podcasts from the phone via the A2DP profile and plays them through the car's sound system. Drivers can directly perform actions like skipping tracks, adjusting volume, and pausing playback using the control buttons on the steering wheel or the central touchscreen, without needing to operate the phone, which helps enhance driving safety.  Furthermore, the car's head unit supports accessing the phone's media library through the AVRCP profile, enabling advanced control functions such as browsing track lists and switching playlists. Additionally, the car screen can synchronously display metadata information like the name of the current track and the artist.

Smart Home and Smart Wearable Devices

In the smart home ecosystem, the collaboration of both protocols enables interconnection and convenient control of audio devices:

1. Smart TV/Set-Top Box: Smart TVs can transmit audio streams via A2DP to Bluetooth speakers or wireless headphones, avoiding interference with others from TV's external sound. Users can use the TV remote control or a smart wristband as an AVRCP controller to control audio playback and obtain information like playback progress and program names from the TV through the AVRCP protocol.

2. Smart Wearable Devices: Smart watches, fitness bands, and other devices can pair with phones to not only receive A2DP audio streams from the phone (some devices support direct playback) but also act as AVRCP controllers to remotely control music playback on the phone.

Office and Entertainment Devices

In office and entertainment scenarios, both protocols enhance the wireless interaction experience of devices:

1. Computers and Wireless Audio Devices: Laptops and desktops transmit audio (like meeting voice, music, video audio) to Bluetooth speakers and wireless headphones via A2DP. Users can control playback using keyboard shortcuts or multimedia buttons on wireless keyboards and mice (AVRCP Controller) or remotely operate computer audio playback via headphone buttons.

2. Gaming Devices: Gaming consoles (such as PS, Xbox) transmit game audio to Bluetooth gaming headphones via A2DP. Players can adjust volume and pause game background music using headphone buttons (AVRCP Controller). Some gaming peripherals also support obtaining in-game audio status information via AVRCP.

Special Scenarios: Medical and Fitness Equipment

In specific professional fields, A2DP/AVRCP have targeted applications:

1. Medical Audio Devices: Bluetooth hearing aids and other hearing assistance devices use A2DP to receive audio streams from phones or medical terminals, helping individuals with hearing impairments clearly access sounds. Simple buttons on the device (as AVRCP controllers) can be used for basic control such as adjusting volume or switching audio.

2. Fitness Equipment: Display devices on treadmills, exercise bikes, and other fitness equipment can connect to a user's Bluetooth headphones via A2DP to play workout music. Users can control music playback directly through the fitness equipment's control panel (as AVRCP controllers) without interrupting their exercise.

Conclusion

Advanced Audio Distribution Profile (A2DP) and Audio/Video Remote Control Profile (AVRCP) are the core of the Bluetooth audio technology system, together forming a "transmission + control" collaborative architecture that provides a standardized solution for the interconnection of various Bluetooth audio devices. With their core advantages, these technologies have become indispensable technical support in fields such as consumer electronics, automotive intelligence, and smart home.

The Realtek SDK has fully integrated A2DP and AVRCP. This SDK implements all roles within the profile and supports coexistence and dynamic switching between roles. This enables products based on Realtek Bluetooth chips to quickly complete various forms of customized development within the existing framework, helping products to seize market opportunities. The Realtek SDK also provides corresponding demo applications for developers to reference during the development process.

For detailed information, please refer to: BR/EDR Audio