Audio Interface Definition

Release History

Release version Date What changed
Pre-14.06 N/A

The following interfaces were added:

  • Stream interface version 1
  • Stream.Port interface version 1
  • Stream.Port.AudioSource interface version 1
  • Stream.Port.AudioSink interface version 1
  • Stream.Port.ImageSource interface version 1
  • Stream.Port.ImageSink interface version 1
  • Stream.Port.Application.MetadataSource interface version 1
  • Stream.Port.Application.MetadataSink interface version 1
  • Stream.Clock interface version 1
14.06 6/30/2014 No updates
14.06 Update 1 9/29/2014
  • Updated the document title and Overview chapter title (changed Specification to Definition).
  • Added the release version number to the document title for version tracking.
  • Added a note in the Definition Overview chapter to address the AllSeen Alliance Compliance and Certification program.
  • Added a Mandatory column for method and signal parameters to support the AllSeen Alliance Compliance and Certification program.
  • Included the object path for each interface.
  • Added the Close method to the Stream interface.

Updated the following data points:

  • Connect method's path parameter signature (o)
  • Pause method's parameter name (timeNanos)
  • Flush method's input parameter name and specified output parameter name (numBytesFlushed)
  • Data signal's parameter name (bytes) for the AudioSource and ImageSource interfaces
  • Data signal's parameter name (dictionary) for the MetadataSource interface
  • AdjustTime method parameter name (adjustNanos)

Separated the following interfaces to address the information unique to the relevant Sink and Source interfaces:

  • Stream.Port.Audio
  • Stream.Port.Image
  • Stream.Port.ApplicationMetadata

Updated the Introspection XML to reflect the Control.Volume output.

14.12 12/17/2014 Cleanup to make requirements for methods and signals more clear.

Definition Overview

A stream consists of one or more elementary streams; an elementary stream consists of one type of media (audio, image, or metadata).

NOTE: All methods and signals are considered mandatory to support the AllSeen Alliance Compliance and Certification program.

Stream Object

A stream object is a BusObject implementing the org.alljoyn.Stream interface. It has one child port object for each elementary stream. A port object is a BusObject implementing the org.alljoyn.Stream.Port interface and one of the media type-specific port interfaces (org.alljoyn.Stream.Port.AudioSink, etc.). Port objects send or receive elementary streams.

Example objects and interfaces used by a speaker

  • /Speaker/In is a stream object
  • /Speaker/In/Audio, /Speaker/In/Image, and /Speaker/In/Metadata are child port objects.
Object path Interfaces implemented
/Speaker/In org.alljoyn.Stream
/Speaker/In/Audio
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.AudioSink
/Speaker/In/Image
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.ImageSink
/Speaker/In/Metadata
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.Application.MetadataSink

Example objects and interfaces used by a media player

Object path Interfaces implemented
/Player/Out org.alljoyn.Stream
/Player/Out/Audio
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.AudioSource
/Player/Out/Image
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.ImageSource
/Player/Out/Metadata
  • org.alljoyn.Stream.Port
  • org.alljoyn.Stream.Port.Application.MetadataSource

The following figure illustrates how source ports are connect to sink ports to enable streaming.

audio-connected-media-player-speaker

Figure: Connected media player and speaker

Typical Stream Flows

One source and one sink

The following figure illustrates a typical call flow for one source and one sink.

audio-one-source-sink

Figure: Typical call flow for one source and one sink

One source and two sinks

The following figure illustrates the typical call flow for one source and two sinks.

audio-one-source-two-sinks

Figure: Typical call flow for one source and two sinks

Discovery

To be discovered by interested client applications on other devices, an audio implementation advertises its existence using the About feature. See the About Feature Interface Definition for more information.

BusObject paths

Implementations of audio should publish the object paths of the BusObjects that implement org.alljoyn.Stream and the object paths of BusObjects that implement the org.alljoyn.Stream.Port interfaces using the org.alljoyn.About interface. See Example objects and interfaces used by a speaker and Example objects and interfaces used by a media player for examples of published BusObjects.

Session port value

In addition to the object paths, the implementation should also publish the session port value that the service uses to listen for incoming client connections. Use this port value in the "port" parameter of the org.alljoyn.About.Announce signal.

Stream Interface

The Stream interface is responsible for stream creation and control over a stream's ports.

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream 1 no Any object path

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-Only Interface version number

Methods

The following methods are exposed by a BusObject that implements the org.alljoyn.Stream interface.

Open

Returns an error if not implemented or called more than once.

Message arguments

None.

Reply arguments

None.

Description

Open the stream.

Close

Returns an error if not implemented or called more than once.

Message arguments

None.

Reply arguments

None.

Description

Close the stream.

Stream.Port Interface

The Stream.Port interface is responsible for control over an elementary stream. A port object implements this interface together with a media-specific port interface such as Stream.Port.AudioSource or Stream.Port.AudioSink.

Interface name Version Secured Object path
org.alljoyn.Stream.Port 1 no Child node of node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number
Direction y
  • 0 - sink
  • 1 - source
Read-only

Indicates if this port is a source or sink port.

Source ports send elementary streams, sink ports receive them.

Capabilities a(sa{sv}) See Media Types for more information. Read-only

Defines the supported capabilities of this port.

The capabilities of unknown media types should be ignored.

Methods

The following methods are exposed by a BusObject that implements the org.alljoyn.Stream.Port interface.

Connect('so(sa{sv})')

Message arguments

Argument Parameter name Signature List of values Description
0 host s AllJoyn name The AllJoyn® name of the remote stream port host to connect to.
1 path o Object path The AllJoyn object path of the remote port on the host to connect to.
2 configuration (sa{sv}) See Media Types A media type and the values to configure its parameters with.

Reply arguments

None.

Description

Connects this port to a remote port and configures the ports to send or receive an elementary stream.

If the configuration is not compatible with the capabilities, this method should return an error.

If this port is already connected to the remote port, this method should return an error. To reconfigure a connected port, first close the stream, then open and connect with the new configuration.

Signals

The following signals are emitted by a BusObject that implements the org.alljoyn.Stream.Port interface.

OwnershipLost('s')

OwnershipLost signal is not a Sessionless signal.

Message arguments

Argument Parameter name Signature List of values Description
0 newOwner s A String AllJoyn name of the new remote port.

Description

The port emits this signal to the currently connected remote port when it connects to a new remote port.

Stream.Port.Audio Interfaces

The Stream.Port.AudioSource and Stream.Port.AudioSink interfaces define the data format for audio/ media. The interfaces are implemented by port objects that support audio/ capabilities.

FIFO control

An audio sink exposes a FIFO to receive streamed data from an audio source. Control of the FIFO is implemented as a state machine. The following figure illustrates the states of the FIFO.

audio-sink-state-diagram

Figure: Audio sink diagram

Filling an audio sink's FIFO is accomplished using the Data signal, FifoSize and FifoPosition properties, and FifoPositionChanged signal. On receipt of each FifoPositionChanged signal, the audio source can send (FifoSize - FifoPosition) more bytes of data. The audio source should not send more than this; doing so can lead to blocking the receipt of other BusMethods and BusSignals by the audio sink, or the audio sink discarding the data.

Use the Flush method to tell the audio sink to discard all the data in its FIFO in preparation for new data.

Synchronization

If an audio sink supports synchronized playback (by implementing the Stream.Clock interface), use the timestamp parameter of the Data signal to determine the correct time to render the data. The audio source computes a timestamp sufficient to ensure that it is greater than the network latency plus the rendering latency of each audio sink. Audio sinks should discard data that cannot be rendered in time.

Stream.Port.AudioSink interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Port.AudioSink 1 no Child node of node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number
FifoSize u Size in bytes Read-only The size of the sink's FIFO in bytes. The size in samples may be computed from the configured Channels, Format, and Rate.
FifiPosition u Position in bytes Read-only The current position of the FIFO in bytes. Bytes read from this position are submitted to the audio device.
Delay (uu)
  • Position in bytes
  • Size in bytes
Read-only

Use the sum of these values and the configured Channels, Format, and Rate properties to compute the delay in seconds from when a sample is received to when it is heard.

  • The first value is FifoPosition.
  • The second value is the size of the audio device's FIFO in bytes.
PlayState y
  • 0 - idle
  • 1 - playing
  • 2 - paused
Read-only The current rendering state.

Methods

The following methods provide control of the audio sink's FIFO state machine.

u Flush('t')

Message arguments

Argument Parameter name Signature List of values Description
0 timeNanos t Timestamp in nanoseconds since the UNIX epoch

Timestamp in nanoseconds since the UNIX epoch to flush at.

  • If an audio sink does not support synchronized playback (by not implementing the Stream.Clock interface), this value should be 0 and the sink should immediately flush.
  • If an audio sink supports synchronized playback, this method should not return a reply until the flush is complete.

Reply arguments

Argument Parameter name Return signature Description
0 numBytesFlushed u Number of bytes flushed from the FIFO. When timeNanos is not 0, this value is the number of bytes flushed after the flush is complete.

Description

Flushes the FIFO of this instance. FifoPositionChanged should be emitted after the flush is complete.

Pause('t')

Mesage arguments

Argument Parameter name Signature List of values Description
0 timeNanos t Timestamp in nanoseconds since the UNIX epoch

Timestamp in nanoseconds since the UNIX epoch to stop rendering data at.

  • If an audio sink does not support synchronized playback (by not implementing the Stream.Clock interface), this value should be 0 and the audio sink should immediately stop rendering.
  • If an audio sink supports synchronized playback, this method should not return a reply until the pause is complete.

Reply arguments

None.

Description

Tell the port to stop rendering data from the FIFO. The FIFO is not flushed.

Play

Message argumemts

None.

Reply arguments

None.

Description

Tells the port to start rendering data from the FIFO.

If the configuration is not compatible with the capabilities, this method should return an error.

Signals

FifoPositionStateChanged

FifoPositionStateChanged is not a Sessionless signal.

Message arguments

None.

Description

An audio sink emits this signal when its FIFO position crosses the low watermark.

PlayStateChanged('yy')

PlayStateChanged is not a Sessionless signal.

Argument Parameter name Signature List of values Description
0 oldState y positive Previous PlayState value.
1 newState y positive Current PlayState value.

Description

Emitted when the PlayState property changes.

Stream/Port.AudioSource Interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Port.Audio 1 no Child node of node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number

Methods

No methods are exposed by this interface.

Signals

Data('tay')

Data signal is not a Sessionless signal.

Argument Parameter name Signature List of values Description
0 timeStamp t positive Timestamp in nanoseconds since the UNIX epoch to render the data. If an audio sink does not support synchronized playback (by not implementing the Stream.Clock interface), this value should be 0.
1 bytes ay array of bytes Interleaved sample data.

Description

This signal is sent by the audio source to the audio sink.

Stream.Port.Image Interfaces

The Stream.Port.ImageSource and Stream.Port.ImageSink interfaces define the data format for image/ media types. The interfaces are implemented by port objects that support image/ capabilities.

Stream.Port.ImageSink interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Port.ImageSink 1 no Child node of the node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number

Methods

No methods are exposed by this interface.

Signals

No signals are emitted by this interface.

Stream.Port.ImageSource interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Port.ImageSource 1 no Child node of the node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers no Interface version number

Methods

No methods are exposed by this interface.

Signals

Data is not a Sessionless signal.

Data('ay')

Message arguments

Argument Parameter name Signature List of values Description
0 bytes ay array of bytes Segment of the image data.

Description

This signal is sent by the source to the sink.

Stream.Port.Application.Metadata Interfaces

The Application.MetadataSource and Application.MetadataSink interfaces define the data format for application/x-metadata media types. The interfaces are implemented by port objects that support the application/x-metadata capability.

Stream.Port.Application.MetadataSink interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Application.MetadataSink 1 no Child node of the node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number

Methods

No methods are exposed by this interface.

Signals

No signals are emitted by this interface.

Stream.Port.Application.MetadataSource interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Port.Application.MetadataSource 1 no Child node of the node implementing the Stream interface.

Properties

Property name Signature List of values Writable Description
Version q Positive integers Read-only Interface version number

Methods

No methods are exposed by this interface.

Signals

Data('a{sv}')

Data is not a Sessionless signal.

Message arguments

Argument Parameter name Signature List of values Description
0 dictionary a{sv} array of pairs of a string and variant Metadata key/value pairs. See Media Types for metadata keys and relevant values.

Description

This signal is sent by the source to the sink.

Control.Volume interface

Interface name

Interface name Version Secured Object path
org.alljoyn.Control.Volume 1 no Must be the same as the path implementing the AudioSink interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number
Volume n Signed integers Read-write Current volume of the device
VolumeRange (nnn)

Signed integers

  • high
  • low
  • step
Read-only

Maximum (high) and minimum (low) values of the volume.

The step value is the incremental unit, the value of Volume is always a multiple of the step.

Mute b
  • true
  • false
Read-write Whether or not this device is muted.
Enabled b
  • true
  • false
Read-only Indicates whether or not Volume control is enabled. If this value is false, all methods that change the playback volume will return an error.

Methods

The following methods are exposed by a BusObject that implements the org.alljoyn.VolumeControl interface.

AdjustVolume('n')

Message arguments

Argument Parameter name Signature List of values Description
0 delta n Signed integer The amount by which to increase or decrease the volume.

Reply arguments

None.

Description

Adjusts the volume by a certain amount. The new volume will be equal to old volume + delta.

AdjustVolumePercent('d')

Message arguments

Argument Parameter name Signature List of values Description
0 change d double precision floating point value

For values greater than 0 and smaller than 1, the percentage by which to raise the volume.

  • For values smaller than 0 and bigger than -1, the percentage by which to reduce the volume.
  • For values greater than or equal to 1, increase volume to maximum.
  • For values smaller than or equal to -1, decrease volume to the minimum.

Reply arguments

None.

Description

Adjusts the volume by a certain percentage.

Signals

VolumeChanged('b')

VolumeChanged signal is not a Sessionless signal.

Message arguments

Argument Parameter name Signature List of values Description
0 newVolume b
  • true
  • false
Emitted when the volume changes

Description

Signal sent when the volume has changed.

MuteChanged('b')

MuteChanged signal is not a Sessionless signal.

Argument Parameter name Signature List of values Description
0 newMute b True or False Emitted when the mute changes to on or off

Description

Signal sent when the volume's mute state has changed.

EnableChanged('b')

EnableChanged signal is not a Sessionless signal.

Argument Parameter name Signature List of values Description
0 enabled b True or False Emitted when when the volume control is enabled or disabled

Description

Signal sent when the volume control is enabled or disabled.

Stream.Clock interface

The Stream.Clock interface provides the ability to set the clock used for synchronized playback. It can be implemented by a stream object.

The following sequence defines the clock synchronization process.

  1. Record the current time as t0.
  2. Call SetTime(t0) and wait for the method reply.
  3. Record the current time as t1.
  4. Call AdjustTime((t1 - t0) / 2).

The maximum error of the clock skew is the value passed to AdjustTime, (t1 - t0) / 2.

Interface name

Interface name Version Secured Object path
org.alljoyn.Stream.Clock 1 no Child node of the node implementing the Stream interface.

Properties

Property name Signature List of values Read/Write Description
Version q Positive integers Read-only Interface version number

Methods

The following methods are exposed by a BusObject that implements the org.alljoyn.Stream.Clock interface.

SetTime('t')

Message arguments

Argument Parameter name Signature List of values Description
0 timeNanos t Timestamp in nanoseconds since the UNIX epoch The time to set the clock used for synchronized playback.

Reply arguments

None.

Description

Sets the time of the clock used for synchronized playback.

AdjustTime('x')

Message arguments

Argument Parameter name Signature List of values Description
0 adjustNanos x Positive or negative time in nanoseconds.

The amount, positive or negative, to adjust the time.

  • For values smaller than 0 and bigger than -1, the percentage by which to reduce the volume.
  • For values greater than or equal to 1, increase volume to maximum.
  • For values smaller than or equal to -1, decrease volume to the minimum.

Reply argments

None.

Description

Adjusts the time of the clock used for synchronized playback forwards or backwards from its current value.

Signals

No signals are emitted by this interface.

Media Types

The following sections define the values of the (sa{sv}) used in the Stream.Port.Capabilities and Stream.Port.Connect interfaces.

  • For a capability, the first parameter of the struct is the media type (such as audio/x-raw). The second parameter is a dictionary of configurable parameters for the media type. The value of the dictionary entry for a configurable parameter is an array of the supported values of the configurable parameter.
  • A configuration is identical to a capability except that the value of the dictionary entry for a configurable parameter is only one of the supported values listed in the capability. In addition to the media types defined below, additional media types may be defined in future revisions of this interface definition or in addition to this interface definition.

audio/x-raw

Raw interleaved PCM data. If audio is supported, this media type is mandatory.

Key Signature List of values Description
Channels y Positive integer Number of channels. Support for 1 and 2 channels is mandatory.
Format s Sample format

Sample formats.

s16le - PCM signed 16-bit wide little endian samples. Support for s16le is mandatory.

Rate q Sample rate Sample rate. Support for 44100 and 48000 sample rates is mandatory.

audio/x-alac

Apple Lossless. Support for this media type is optional.

Key Signature List of values Description
Channels y Positive integer Number of channels. Support for 1 and 2 channels is mandatory.
Format s Sample format

Sample formats.

s16le - PCM signed 16-bit wide little endian samples. Support for s16le is mandatory.

Rate q Sample rate Sample rate. Support for 44100 and 48000 sample rates is mandatory.
MagicCookie ay Array of bytes Magic cookie. Used only in configuration.
FramesPerPacket u Frames per packet Frames per packet. Used only in configuration.

image/jpeg

JPEG image data. Support for this media type is optional.

application/x-metadata

Stream metadata. Support for this media type is optional.

Media Item Keys

The following table lists the keys and values that can be used in a metadata dictionary entry.

Date values are to only be represented as strings in one of the following ISO 8601 formats:

  • Year only: "<year>" where <year> includes all digits of the year.
  • Date: "<year><month><day>" where:
    • <year> includes all digits of the year
    • <month> is a 2-digit representation of month ("01" = January)
    • <day> is the day of the month (e.g., "09").
  • Date and time: "<year><month><day>T<hour><minute><second>+/-<offset>" where:
    • <year>, <month>, and <day> are the same as the date previously specified
    • <hour> is the hour ("00" through "23")
    • <minute> is the minute ("00" through "59")
    • <second> is the second ("00" through "59")
    • <offset> is the offset from UTC ("-0800" corresponds to Pacific Standard Time)
  • Date and time: "<year><month><day>T<hour><minute>+/-<offset>" is the same as the previous date and time specification except without the (seconds) portion.
Key Signature List of values Description
Name s N/A Name or title of the item
Album s N/A Album title
AlbumArtist s N/A Album artist
AlbumRating y 0-5 "Start" rating
Artist s N/A Artist that performed the item
Bpm g N/A Beats per minute
Compilation b N/A Indicates if item is part of a compilation
Composer s N/A Composer of the item
DiscCount g N/A Total number of discs in a multi-disc release
DiscNumber g N/A Disc number in a multi-disc release
Duration u N/A Duration of the item in milliseconds
Genre s N/A Genre of the item
Rating y 0-5 "Star" rating
ReleaseDate s Date Date item was first released
TrackCount g N/A Total number of tracks on the album
TrackNumber g N/A Track number of the item within the album

Introspection XML

<node xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:noNamespaceSchemaLocation="http://www.allseenalliance.org/schemas/introspect.xsd">

   <interface name="org.alljoyn.Stream">
      <property name="Version" type="q" access="read"/>
      <method name="Open"/>
      <method name="Close"/>
   </interface>

   <interface name="org.alljoyn.Stream.Port">
      <property name="Version" type="q" access="read"/>
      <property name="Direction" type="y" access="read"/>
      <property name="Capabilities" type="a(sa{sv})" access="read"/>
      <signal name="OwnershipLost">
         <arg name="newOwner" type="s"/>
      </signal>
      <method name="Connect">
         <arg name="host" type="s" direction="in"/>
         <arg name="path" type="o" direction="in"/>
         <arg name="configuration" type="(sa{sv})" direction="in"/>
      </method>
   </interface>

   <interface name="org.alljoyn.Stream.Port.AudioSink">
      <property name="Version" type="q" access="read"/>
      <property name="FifoSize" type="u" access="read"/>
      <property name="FifoPosition" type="u" access="read"/>
      <property name="Delay" type="(uu)" access="read"/>
      <signal name="FifoPositionChanged"/>
      <property name="PlayState" type="y" access="read"/>
      <signal name="PlayStateChanged">
         <arg name="oldState" type="y"/>
         <arg name="newState" type="y"/>
      </signal>
      <method name="Play"/>
      <method name="Pause">
         <arg name="timeNanos" type="t" direction="in"/>
      </method>
      <method name="Flush">
         <arg name="timeNanos" type="t" direction="in"/>
         <arg name="numBytesFlushed" type="u" direction="out"/>
      </method>
   </interface>

   <interface name="org.alljoyn.Stream.Port.AudioSource">
      <property name="Version" type="q" access="read"/>
      <signal name="Data">
         <arg name="timestamp" type="t"/>
         <arg name="bytes" type="ay"/>
      </signal>
   </interface>

   <interface name="org.alljoyn.Stream.Port.ImageSink">
      <property name="Version" type="q" access="read"/>
   </interface>

   <interface name="org.alljoyn.Stream.Port.ImageSource">
      <property name="Version" type="q" access="read"/>
      <signal name="Data">
         <arg name="bytes" type="ay"/>
      </signal>
   </interface>

   <interface name="org.alljoyn.Stream.Port.Application.MetadataSink">
      <property name="Version" type="q" access="read"/>
   </interface>

   <interface name="org.alljoyn.Stream.Port.Application.MetadataSource">
      <property name="Version" type="q" access="read"/>
      <signal name="Data">
         <arg name="dictionary" type="a{sv}"/>
      </signal>
   </interface>

   <interface name="org.alljoyn.Stream.Clock">
      <property name="Version" type="q" access="read"/>
      <method name="SetTime">
         <arg name="timeNanos" type="t" direction="in"/>
      </method>
      <method name="AdjustTime">
         <arg name="adjustNanos" type="x" direction="in"/>
      </method>
   </interface>

   <interface name="org.alljoyn.Control.Volume">
      <property name="Version" type="q" access="read"/>
      <property name="Volume" type="n" access="readwrite"/>
      <property name="VolumeRange" type="(nnn)" access="read"/>
      <property name="Mute" type="b" access="readwrite"/>
      <signal name="VolumeChanged">
         <arg name="newVolume" type="n"/>
         <signal name="MutedChanged">
         <arg name="newMute" type="b"/>
      </signal>
      <method name="AdjustVolume">
         <arg name="delta" type="n" direction="in"/>
      </method>
      <method name="AdjustVolumePercent">
         <arg name="change" type="d" direction="in"/>
      </method>
      <property name="Enabled" type="b" access="read"/>
      <signal name="EnableChanged">
         <arg name="enabled" type="b"/>
      </signal>
   </interface>


</node>