PJMEDIA Audio Device API

Table of Contents

1. Background
2. Features

The PJMEDIA Audio Device API is a new sound device abstraction API/library in PJMEDIA, introduced in PJSIP version 1.1, deprecating the ​existing sound device API.

Background

The PJMEDIA Audio Device API was introduced as part of the implementation of APS-Direct implementation in PJSIP version 1.1. During the design and implementation of APS-Direct project, it was clear that the ​existing sound device API lacks many features that are needed to support the project. We had the choice to either patch the existing API with new features that are specific to Nokia APS, and potentially break existing applications anyway, or design a new sound device API to support all these new features as well as future enhancements, while providing some support for the old sound API and a clear migration path to the new API.

Features

The new audio device API contains the following major features.

Forward compatibility:

The new API has been designed to be extensible, it will support new API's as well as new features that may be introduced in the future without breaking compatibility with applications that use this API.

Device capabilities:

At the heart of the API is device capabilities management, where all possible audio capabilities of audio devices should be able to be handled in a generic manner. With this framework, new capabilities that may be discovered in the future can be handled in manner without breaking existing applications.

Built-in features:

The device capabilities framework enables applications to use audio features built-in in the device, such as echo cancellation, built-in codecs, audio routing, and volume control.

Codec support:

Some audio devices such as Nokia/Symbian? Audio Proxy Server (APS) and Nokia VoIP Audio Services (VAS) support built-in hardware audio codecs (e.g. G.729, iLBC, and AMR), and this feature is supported by the new audio device API.