Bluetooth Audio Plugin

Version: 1.0

Status:

BluetoothAudio plugin for Thunder framework.

Table of Contents

• Introduction
• Description
• Configuration
• Interfaces
• Methods
• Properties
• Notifications

Introduction

Scope

This document describes purpose and functionality of the BluetoothAudio plugin. It includes detailed specification about its configuration, methods and properties as well as sent notifications.

Case Sensitivity

All identifiers of the interfaces described in this document are case-sensitive. Thus, unless stated otherwise, all keywords, entities, properties, relations and actions should be treated as such.

Acronyms, Abbreviations and Terms

The table below provides and overview of acronyms used in this document and their definitions.

Acronym	Description
API	Application Programming Interface
BR/EDR	Basic Rate/Enhanced Data Rate
HTTP	Hypertext Transfer Protocol
JSON	JavaScript Object Notation; a data interchange format
JSON-RPC	A remote procedure call protocol encoded in JSON
LC-SBC	Low-Complexity SubBand Coding

The table below provides and overview of terms and abbreviations used in this document and their definitions.

Term	Description
bitpool	A parameter to the LC-SBC codec that changes the encoding bitrate; the higher it is the higher the bitrate and thus the audio quality
callsign	The name given to an instance of a plugin. One plugin can be instantiated multiple times, but each instance the instance name, callsign, must be unique.

References

Ref ID	Description
HTTP	HTTP specification
JSON-RPC	JSON-RPC 2.0 specification
JSON	JSON specification
Thunder	Thunder API Reference

Description

The Bluetooth Audio Sink plugin enables audio streaming to Bluetooth audio sink devices. The plugin is sink a from the host device stack perspective; in Bluetooth topology the host device becomes in fact an audio source. The plugin requires a Bluetooth controller service that will provide Bluetooth BR/EDR scanning, pairing and connection functionality; typically this is fulfiled by the BluetoothControl plugin.

The plugin is designed to be loaded and executed within the Thunder framework. For more information about the framework refer to [Thunder].

Configuration

The table below lists configuration options of the plugin.

Name	Type	M/O	Description
callsign	string	mandatory	Plugin instance name (default: BluetoothAudio)
classname	string	mandatory	Class name: BluetoothAudio
locator	string	mandatory	Library name: libThunderBluetoothAudio.so
startmode	string	mandatory	Determines in which state the plugin should be moved to at startup of the framework
controller	string	optional	Callsign of the Bluetooth controller service (typically BluetoothControl)
server	object	optional	BluetoothAudio server configuration
server?.interface	integer	optional	Bluetooth interface to listen to for incomming connections
server?.inactivitytimeout	integer	optional	Timeout to drop inactive connections (in ms)
server?.psm	integer	optional	Port to listen to for incomming conections (typically 25)
sink	object	optional	BluetoothAudio sink configuration
sink.codecs	object	mandatory	Codec settings
sink.codecs.LC-SBC	object	mandatory	Settings for the LC-SBC codec
sink.codecs.LC-SBC?.preset	string	optional	Predefined audio quality setting (must be one of the following: Compatible, HQ, LQ, MQ, XQ)
sink.codecs.LC-SBC?.bitpool	integer	optional	Custom audio quality based on bitpool value (used when preset is not specified)
sink.codecs.LC-SBC?.channelmode	string	optional	Channel mode for custom audio quality (used when preset is not specified) (must be one of the following: DualChannel, JointStereo, Mono, Stereo)
source	object	optional	BluetoothAudio source configuration
source.codecs	object	mandatory	Codec settings
source.codecs?.LC-SBC	object	optional	Settings for the LC-SBC codec
source.codecs?.LC-SBC.maxbitpool	integer	mandatory	Maximum accepted bitpool value

Interfaces

This plugin implements the following interfaces:

• IBluetoothAudio::ISink (IBluetoothAudio.h) (version 1.0.0) (compliant format)

  This interface uses legacy lowercase naming convention. With the next major release the naming convention will change to camelCase.

• IBluetoothAudio::ISource (IBluetoothAudio.h) (version 1.0.0) (compliant format)

  This interface uses legacy lowercase naming convention. With the next major release the naming convention will change to camelCase.

Methods

The following methods are provided by the BluetoothAudio plugin:

BluetoothAudio Sink interface methods:

Method	Description
sink::assign	Assigns a Bluetooth sink device for audio playback
sink::revoke	Revokes a Bluetooth sink device from audio playback

sink::assign ^method

Assigns a Bluetooth sink device for audio playback.

Parameters

Name	Type	M/O	Description
params	object	mandatory	...
params.address	string	mandatory	Address of the bluetooth device to assign

Result

Name	Type	M/O	Description
result	null	mandatory	Always null

Errors

Message	Description
ERROR_BAD_REQUEST	Device address value is invalid
ERROR_ALREADY_CONNECTED	A sink device is already assigned

Example

Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::assign",
  "params": {
    "address": "..."
  }
}

Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": null
}

sink::revoke ^method

Revokes a Bluetooth sink device from audio playback.

Parameters

This method takes no parameters.

Result

Name	Type	M/O	Description
result	null	mandatory	Always null

Errors

Message	Description
ERROR_ALREADY_RELEASED	No device is currently assigned as sink

Example

Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::revoke"
}

Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": null
}

Properties

The following properties are provided by the BluetoothAudio plugin:

BluetoothAudio Sink interface properties:

Property	R/W	Description
sink::state	read-only	Current state o the audio sink device
sink::device	read-only	Bluetooth address of the audio sink device
sink::type	read-only	Type of the audio sink device
sink::latency	read/write	Latency of the audio sink device
sink::supportedcodecs	read-only	Audio codecs supported by the audio sink device
sink::supporteddrms	read-only	DRM schemes supported by the audio sink device
sink::codec	read-only	Properites of the currently used audio codec
sink::drm	read-only	Properites of the currently used DRM scheme
sink::stream	read-only	Properties of the currently transmitted audio stream

BluetoothAudio Source interface properties:

Property	R/W	Description
source::state	read-only	Current state of the source device
source::device	read-only	Bluetooth address of the source device
source::type	read-only	Type of the audio source device
source::codec	read-only	Properites of the currently used codec
source::drm	read-only	Properties of the currently used DRM scheme
source::stream	read-only	Properites of the currently transmitted audio stream

sink::state ^property

Provides access to the current state o the audio sink device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Current state o the audio sink device (must be one of the following: Connected, ConnectedBad, ConnectedRestricted, Connecting, Disconnected, Ready, Streaming, Unassigned)

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::state"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "Disconnected"
}

sink::device ^property

Provides access to the bluetooth address of the audio sink device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Bluetooth address of the audio sink device

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not assigned

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::device"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "..."
}

sink::type ^property

Provides access to the type of the audio sink device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Type of the audio sink device (must be one of the following: Amplifier, Headphone, Recorder, Speaker, Unknown)

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not connected

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::type"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "Headphone"
}

sink::latency ^property

Provides access to the latency of the audio sink device.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Latency of the audio sink device
(property).value	integer	mandatory	Audio latency in milliseconds

Name	Type	M/O	Description
(property)	integer	mandatory	Latency of the audio sink device

Errors

Message	Description
ERROR_BAD_REQUEST	Latency value is invalid

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::latency"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": 0
}

Set Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::latency",
  "params": {
    "value": 20
  }
}

Set Response

{
    "jsonrpc": "2.0",
    "id": 42,
    "result": "null"
}

sink::supportedcodecs ^property

Provides access to the audio codecs supported by the audio sink device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	array	mandatory	Audio codecs supported by the audio sink device
(property)[#]	string	mandatory	... (must be one of the following: LC-SBC)

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not connected

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::supportedcodecs"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": [
    "LC-SBC"
  ]
}

sink::supporteddrms ^property

Provides access to the DRM schemes supported by the audio sink device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	array	mandatory	DRM schemes supported by the audio sink device
(property)[#]	string	mandatory	... (must be one of the following: DTCP, SCMS-T)

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not connected

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::supporteddrms"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": [
    "SCMS-T"
  ]
}

sink::codec ^property

Provides access to the properites of the currently used audio codec.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properites of the currently used audio codec
(property).codec	string	mandatory	Audio codec used (must be one of the following: LC-SBC)
(property).settings	opaque object	mandatory	Codec-specific audio quality preset, compression profile, etc

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::codec"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "codec": "LC-SBC",
    "settings": {}
  }
}

sink::drm ^property

Provides access to the properites of the currently used DRM scheme.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properites of the currently used DRM scheme
(property).drm	string	mandatory	Content protection scheme used (must be one of the following: DTCP, SCMS-T)
(property).settings	opaque object	mandatory	DRM-specific content protection level, encoding rules, etc

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not connected or not yet configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::drm"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "drm": "SCMS-T",
    "settings": {}
  }
}

sink::stream ^property

Provides access to the properties of the currently transmitted audio stream.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properties of the currently transmitted audio stream
(property).samplerate	integer	mandatory	Sample rate in Hz
(property).bitrate	integer	mandatory	Target bitrate in bits per second (eg. 320000)
(property).channels	integer	mandatory	Number of audio channels
(property).resolution	integer	mandatory	Sampling resolution in bits per sample
(property).isresampled	boolean	mandatory	Indicates if the source stream is being resampled by the stack to match sink capabilities

Errors

Message	Description
ERROR_ILLEGAL_STATE	The sink device currently is not connected or not yet configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.sink::stream"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "samplerate": 44100,
    "bitrate": 0,
    "channels": 2,
    "resolution": 16,
    "isresampled": false
  }
}

source::state ^property

Provides access to the current state of the source device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Current state of the source device (must be one of the following: Connected, ConnectedBad, ConnectedRestricted, Connecting, Disconnected, Ready, Streaming, Unassigned)

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::state"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "Disconnected"
}

source::device ^property

Provides access to the bluetooth address of the source device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Bluetooth address of the source device

Errors

Message	Description
ERROR_ILLEGAL_STATE	No source device is currently connected

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::device"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "..."
}

source::type ^property

Provides access to the type of the audio source device.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	string	mandatory	Type of the audio source device (must be one of the following: Microphone, Mixer, Player, Tuner, Unknown)

Errors

Message	Description
ERROR_ILLEGAL_STATE	No source device is currently connected

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::type"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": "Player"
}

source::codec ^property

Provides access to the properites of the currently used codec.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properites of the currently used codec
(property).codec	string	mandatory	Audio codec used (must be one of the following: LC-SBC)
(property).settings	opaque object	mandatory	Codec-specific audio quality preset, compression profile, etc

Errors

Message	Description
ERROR_ILLEGAL_STATE	No source device is not connected or sink is not yet configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::codec"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "codec": "LC-SBC",
    "settings": {}
  }
}

source::drm ^property

Provides access to the properties of the currently used DRM scheme.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properties of the currently used DRM scheme
(property).drm	string	mandatory	Content protection scheme used (must be one of the following: DTCP, SCMS-T)
(property).settings	opaque object	mandatory	DRM-specific content protection level, encoding rules, etc

Errors

Message	Description
ERROR_ILLEGAL_STATE	No source device is connected or sink is not yet configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::drm"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "drm": "SCMS-T",
    "settings": {}
  }
}

source::stream ^property

Provides access to the properites of the currently transmitted audio stream.

This property is read-only.

Value

Name	Type	M/O	Description
(property)	object	mandatory	Properites of the currently transmitted audio stream
(property).samplerate	integer	mandatory	Sample rate in Hz
(property).bitrate	integer	mandatory	Target bitrate in bits per second (eg. 320000)
(property).channels	integer	mandatory	Number of audio channels
(property).resolution	integer	mandatory	Sampling resolution in bits per sample
(property).isresampled	boolean	mandatory	Indicates if the source stream is being resampled by the stack to match sink capabilities

Errors

Message	Description
ERROR_ILLEGAL_STATE	No source device is connected or sink is not yet configured

Example

Get Request

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.source::stream"
}

Get Response

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "samplerate": 44100,
    "bitrate": 0,
    "channels": 2,
    "resolution": 16,
    "isresampled": false
  }
}

Notifications

Notifications are autonomous events triggered by the internals of the implementation and broadcasted via JSON-RPC to all registered observers. Refer to [Thunder] for information on how to register for a notification.

The following events are provided by the BluetoothAudio plugin:

BluetoothAudio Sink interface events:

Notification	Description
sink::statechanged	Signals audio sink state change

BluetoothAudio Source interface events:

Notification	Description
source::statechanged	Signals audio source state change

sink::statechanged ^notification

Signals audio sink state change.

Notification Parameters

Name	Type	M/O	Description
params	object	mandatory	...
params.state	string	mandatory	Changed BluetoothAudio State (must be one of the following: Connected, ConnectedBad, ConnectedRestricted, Connecting, Disconnected, Ready, Streaming, Unassigned)

Example

Registration

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.register",
  "params": {
    "event": "sink::statechanged",
    "id": "myid"
  }
}

Notification

{
  "jsonrpc": "2.0",
  "method": "myid.sink::statechanged",
  "params": {
    "state": "Disconnected"
  }
}

The client ID parameter is passed within the notification designator, i.e. <client-id>.sink::statechanged.

source::statechanged ^notification

Signals audio source state change.

Notification Parameters

Name	Type	M/O	Description
params	object	mandatory	...
params.state	string	mandatory	Changed BluetoothAudio State (must be one of the following: Connected, ConnectedBad, ConnectedRestricted, Connecting, Disconnected, Ready, Streaming, Unassigned)

Example

Registration

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "BluetoothAudio.1.register",
  "params": {
    "event": "source::statechanged",
    "id": "myid"
  }
}

Notification

{
  "jsonrpc": "2.0",
  "method": "myid.source::statechanged",
  "params": {
    "state": "Disconnected"
  }
}

The client ID parameter is passed within the notification designator, i.e. <client-id>.source::statechanged.