From OpenHome

Revision as of 13:31, 2 June 2011

Introduction

OpenHome Av is an independent standard for networked audio visual devices. OpenHome Av products all have a standard way of presenting themselves to the network. This makes it possible to write generic Control Point software that is able to control those products independent of manufacturer or specific features.

The technologies associated with making this possible are grouped under the term OpenHome Av Topology.

If a developer wishes to write generic software that participates in the aims described above, then they should write that software in a way that conforms to the strategies and algorithms of OpenHome Av Topology, which is described below

Topology

Products

An OpenHome installation consists of products from a variety of manufacturers each bearing the Product service.

Amongst other information, each product has:

• Room (user configurable, defaults to 'Main Room')

• Name (user configurable, defaults to the model name)

• Source Count (fixed according to the capabilities of the product)

• List of Sources, each with its own Type, Name, and Visibility

• Attributes, identifying additional functionality offered by the product

Proper Configuration

The name of each product represents its audio output.

The name of each source represents an audio input (either internal or external).

In a properly configured system, if one product is connected to another using an audio cable, then the name of the product sending the audio should match the name of the source receiving the audio. It is by matching these names that a Control Point is able to select the correct input on, for instance, a preamp when a particular source is selected.

Discovering An OpenHome Av System

The correct way to discover an OpenHome Av system is to:

• search for all units bearing the Product service

• subscribe to each Product service

• group these products according to their Room.

• collect the name of all the sources in each product

• match the names of the sources to the names of the products to create a set of tree structures in each room.

Source Functionality

To determine the kind of functionality available on each source, inspect its type.

If it has type Playlist, it additionally contains the Playlist service

If it has type Radio, it additionally contains the Radio service

If it has type Receiver, it additionally contains the Receiver service

Volume Control

Products that offer volume control include the Volume attribute and the Volume service

The primary volume control offered by a control point should be the one situated nearest the root in the tree structure that contains the current source.

Control points may optionally provide the user with control of the volume of each product within the tree.

Now Playing Information

Products that provide information concerning the currently playing media include the Info service

Products that report the duration of the currently playing track include the Time service

Multiroom Functionality

The Sender service indicates the presence of an OpenHome Av sender and provides information concerning that sender.

An OpenHome Av sender broadcasts music on a network in a way that is playable by an OpenHome Av receiver.

The Receiver service provides the means for controlling a Receiver source. If a device's Product service reports a source of type 'Receiver', then that device is guaranteed to bear the Receiver service.

Services

• Product service
• Playlist service
• Radio service
• Info service
• Time service
• Volume service
• Sender service
• Receiver service

Songcast Specifications

• Songcast OHM/OHU Protocol Specification
• Songcast OHZ Protocol Specification