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The DevSound API provides the interface between Symbian OS and the audio processing hardware for all audio functionality. DevSound is responsible for providing access to audio resources, configuring audio hardware, and audio playback and recording.
This functionality is provided by the CMMFDevSound
class.
DevSound provides a common API for all audio functionality. Shown below is a representation of how the DevSound component interacts with the MMF Controller Framework and other components:
DevSound uses the following components:
Client - DevSound can be used by the following clients:
applications
third party / licensee library.
MMF Controller Framework
For audio playing, recording, and conversion, the MMF client APIs
interact with the lower levels of the MMF, the controller framework. The
controller framework helps to manage the interface to DevSound and provides
controller plug-ins for playing, recording, and converting audio data. The
controller framework has two main classes RMMFController
and CMMFController
.
Controller Plug-in
Depending on the functionality required by the client, the MMF controller framework loads the appropriate controller plug-ins. The plug-ins perform the required operations by communicating with DevSound and/or DevVideo, codecs and hardware.
Custom controller plug-ins can be written to extend the MMF framework. For more information, see How to write a controller plug-in.
Audio Policy
The Audio Policy component manages requests to access the audio hardware. For example, if DevSound needs to acquire the hardware for playing audio, it makes a request to the Audio Policy component. Depending on the priority of the request, the Audio Policy component grants or denies access to the hardware. DevSound must obey the Audio Policy.
Codecs
DevSound uses codecs to convert multimedia data between different encodings.
Custom codec plug-ins can be written. For more information, see How to write a codec plug-in.
Hardware Device API
For audio functionality, the CMMFHwDevice
plug-in class acts as the DevSound interface to the audio processing hardware.
The DevSound API offers the following main functions which can be used by DevSound clients:
Audio Settings
DevSound can be used to initialise and configure hardware devices, for example, set microphone gain and stereo balance.
Audio Play
DevSound can be used to play buffered audio data.
Audio Record
DevSound can be used to record audio data.
Audio Convert
DevSound can be used to convert the type, sample rate and format of audio data.
Tone Play
DevSound can play a single tone, tone sequence or Dual Tone Multi-Frequency (DTMF) string.
The DevSound API comprises the following classes:
CMMFDevSound
is the class which forms the
DevSound API.
MDevSoundObserver
provides callbacks to
users of the DevSound API. It serves as the method of communication between a
client and DevSound. For example, MDevSoundObserver
handles completion and cancellation requests for audio playing, recording, and
conversion.