Over Bluetooth, devices can transmit data that can be used for
interactive services such as audio, messaging, and telephony. The
Bluetooth profiles used for different services can be found in
include/hardware/bluetooth.h.
Audio
A Bluetooth connection lets users stream audio on Bluetooth-enabled devices. For most audio use cases, the Android device is the source, and the rendering device, such as a speaker or a headset, is the sink.
Absolute volume control
In Android 6.0 and later, the Android Bluetooth stack lets a source set an absolute volume, giving users accurate control over audio volume. The source device sends un-attenuated audio and volume information to the sink. The sink then amplifies the audio according to the volume information, so users hear accurate playback volume.
The source device can also register volume notifications. When volume changes are made with controls on the sink, the sink sends a notification to the source. This lets the source accurately display volume information on a user interface.
Absolute volume control is on by default. To disable absolute volume control, users can go to Settings > System > Developer options and select the toggle for Disable absolute volume.
Advanced audio codecs
In Android 8.0, devices that use the Advanced Audio Distribution Profile (A2DP) can support additional audio codecs. The Bluetooth stack supports audio codec negotiation for when devices connect to a remote audio sink. This negotiation selects the best codec supported by both the sender and the sink to provide high-quality audio. After selection, all audio is routed through the selected encoder and then sent to the sink.
Implementation
Devices running Android 8.0 that support A2DP automatically gain the additional codec support. Device manufacturers may need to obtain separate licenses and binary blobs for some proprietary audio codecs. In addition to SBC, Android 8.0 supports the following codecs:
- AAC
- aptX
- aptX HD
- LDAC
Device manufacturers can choose which codecs their devices
attempt to use first. Set the codec priorities by changing the
following values in
res/values/config.xml:
<!-- Configuring priorities of A2DP source codecs. Larger value means
higher priority. Value -1 means the codec is disabled.
Value 0 is reserved and should not be used here. Enabled codecs
should have priorities in the interval [1, 999999], and each
priority value should be unique. -->
<integer name="a2dp_source_codec_priority_sbc">1001</integer>
<integer name="a2dp_source_codec_priority_aac">2001</integer>
<integer name="a2dp_source_codec_priority_aptx">3001</integer>
<integer name="a2dp_source_codec_priority_aptx_hd">4001</integer>
<integer name="a2dp_source_codec_priority_ldac">5001</integer>
LDAC certification
The Android Open Source Project includes an encoder for Sony's LDAC codec, so a separate license or blob from Sony is not needed for it. To integrate the LDAC codec into your device, register with Sony and follow the LDAC certification process.
The LDAC certification website has documentation about LDAC, such as specification and operation handbooks. The LDAC site also provides validation and interoperability tests for mobile and tablet devices. Send passing test results to Sony to complete LDAC certification.
UI features
Along with additional codec support, Android 8.0 provides a user-facing setting to disable high-definition (HD) Bluetooth audio codecs.
- Navigate to Settings > Connected devices > Bluetooth.
- Tap on the gear icon next to the sink you want to disable codecs for.
- Uncheck the HD Audio checkbox.
Device manufacturers that customize Settings should implement a way for users to disable HD codecs.
Messaging
Messaging over Bluetooth lets users read, browse, and compose SMS messages from a remote device. This capability is often used when connecting a phone to an in-vehicle infotainment system.
Telephony
Bluetooth telephony services lets users stream calls and sync contacts from a phone to another Bluetooth device. These features are often used for hands-free calls when driving.
In Android 8.0, Bluetooth supports in-band ringtone. When a phone connected over Bluetooth receives an incoming call, the ringtone will play on the sink. Enable in-band ringtone in Settings > System > Developer options by selecting the toggle for Enable in-band ringing.
Bluetooth features
To implement the Bluetooth services, the Bluetooth stack supports a variety of profiles and features.
Bluetooth profiles
These profiles are available for Bluetooth:
| Feature | Android version | |||||
|---|---|---|---|---|---|---|
| Name | Description | 6.0 | 7.0 | 7.1 | 7.1.2 | 8.0 |
| SAP | SIM Access Profile | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 |
| MAP | Message Access Profile for SMS | 1.2 | 1.2 | 1.2 | 1.2 | 1.2 |
| OPP | Object Push Profile | 1.1 | 1.1 | 1.1 | 1.1 | 1.2 |
| OBEX over L2CAP | OBject EXchange over Logical Link Control and Adaptation Protocol | Yes | Yes | Yes | Yes | Yes |
| HFP Audio Gateway | Hands-Free Profile | 1.6 | 1.6 | 1.7 | 1.7 | 1.7 |
| HSP | Headset Profile | 1.2 | 1.2 | 1.2 | 1.2 | 1.2 |
| A2DP | Advanced Audio Distribution Profile | 1.2 | 1.2 | 1.2 | 1.2 | 1.2 |
| AVRCP | Audio/Video Remote Control Profile | 1.3 | 1.3 | 1.3 | 1.3 | 1.4 |
| HID | Human Interface Device Profile | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| PBAP | Phone Book Access Profile | 1.1.1 | 1.1.1 | 1.1.1 | 1.1.1 | 1.2 |
| HDP | Health Device Profile | 1.0 | 1.0 | 1.1 | 1.1 | 1.1 |
| SPP | Serial Port Profile | 1.2 | 1.2 | 1.2 | 1.2 | 1.2 |
| PAN / BNEP | Personal Area Networking Profile / Bluetooth Network Encapsulation Protocol | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| DIP | Device ID Profile | 1.3 | 1.3 | 1.3 | 1.3 | 1.3 |
| HOGP 1.0 | HID over GATT | Yes | Yes | Yes | Yes | Yes |
| HD Audio1 | See "Advanced audio codecs" above | No | No | No | No | Yes |
1 Implementing HD Audio depends on device capabilities, both on the source and the sink.
Bluetooth Low Energy features
These features are available for BLE:
| Feature | Android version | ||||
|---|---|---|---|---|---|
| Name | 6.0 | 7.0 | 7.1 | 7.1.2 | 8.0 |
| BR/EDR secure connections | 4.1 | 4.1 | 4.1 | 4.1 | 5.0 |
| LE Privacy | 4.2 | 4.2 | 4.2 | 4.2 | 5.0 |
| LE secure connections | 4.2 | 4.2 | 4.2 | 4.2 | 5.0 |
| Data Packet Extensions | 4.2 | 4.2 | 4.2 | 4.2 | 5.0 |
| 32-bit UUIDs | Yes | Yes | Yes | Yes | Yes |
| Dual Mode LE Central/Peripheral | Yes | Yes | Yes | Yes | Yes |
| LE Peripheral Mode | Yes | Yes | Yes | Yes | Yes |
| Google HCI Requirements | Yes | Yes | Yes | Yes | Yes |
| LE Connection-Oriented Channels | No | No | No | No | No |