Initializing +DevSound Functionality Tutorial

+ +

Required background

Before +you start, you must:

Understand the A3F DevSound Component to +which the DevSound library belongs.
Understand the architectural +relationship of the DevSound. For information see DevSound +Overview.

Introduction

DevSound's functionality is provided +by the CMMFDevSound class.

Construction +and initialization

Each client using audio resources must have +an instance of the CMMFDevSound class associated with it. +The CMMFDevSound::NewL() method is used to construct a +new instance of DevSound.

static IMPORT_C CMMFDevSound *NewL();

Once +created, the CMMFDevSound::InitializeL() method is used +to initialize DevSound to play and record. There are three versions of the CMMFDevSound::InitializeL() method, +differing in type and number of parameters. The three versions are:

CMMFDevSound::InitializeL() - +initializes CMMFDevSound object to play and record PCM16 raw audio data with +sampling rate of 8 KHz.
IMPORT_C void InitializeL(MDevSoundObserver &aDevSoundObserver, TMMFState +aMode);
This method has two parameters:
- MDevSoundObserver - +a reference to a DevSound Observer instance.
- TMMFState - +the mode for which this object is to be used, for example, EMMFStatePlaying.
CMMFDevSound::InitializeL() - +initializes DevSound object for the mode aMode for processing +audio data with hardware device aHWDev.
IMPORT_C void InitializeL(MDevSoundObserver &aDevSoundObserver, TUid aHWDev, +TMMFState aMode);
This method has three parameters:
- MDevSoundObserver - +a reference to a DevSound Observer instance.
- TUid - +the CMMFHwDevice implementation identifier.
- TMMFState - +the mode for which this object is to be used, for example, EMMFStatePlaying.
CMMFDevSound::InitializeL() - +initializes DevSound object for the mode aMode for processing +audio data with hardware device supporting FourCC aDesiredFourCC.
IMPORT_C void InitializeL(MDevSoundObserver &aDevSoundObserver, TFourCC +aDesiredFourCC, TMMFState aMode);
This method has three parameters:
- MDevSoundObserver - +a reference to a DevSound Observer instance.
- TFourCC - +the CMMFHwDevice implementation FourCC code.
- TMMFState - +the mode for which this object is to be used, for example, EMMFStatePlaying.

All versions of CMMFDevSound::InitializeL() require +a reference to a DevSound Observer instance. As soon as initialization of +DevSound has completed, successfully or otherwise, the callback function MDevSoundObserver::InitializeComplete() is +called.

The +DevSound Observer

Most methods in the CMMFDevSound class are asynchronous. +Callbacks occur through the MDevSoundObserver class. MDevSoundObserver is +an interface to a set of DevSound callback functions. It serves as the method +of communication between the client and the DevSound. A class that uses DevSound +will typically inherit from MDevSoundObserver.

MDevSoundObserver handles +the MDevSoundObserver::InitializeComplete() initialization +completion event.

Purpose

Refer to the following sections for detailed +information on how to use the main features of DevSound:

Playing +Audio
Recording +Audio
Playing +Tones

Example uses

These examples describe some different +uses of DevSound:

Recording +a WAV file

In this example, a client application wants to record +a WAV file. As WAV is a standard file format supported by the MMF controller +framework, the CMdaAudioRecorderUtility client API is used +to interact with DevSound.

The main steps in recording the WAV file +are:

The client application +gives a request to record to the MMF CMdaAudioRecorderUtility client +API.
The MMF CMdaAudioRecorderUtility client +API passes the command down through the controller framework to the MMF controller +plug-in.
The MMF controller plug-in +initializes DevSound for recording.
Recording starts and +continues until the client stops the recording or the limit on the file size +is reached.
Upon completion, the +client gives a request to the MMF controller framework to stop the recording. +The controller framework passes the command down to the MMF controller plug-in.
The MMF controller plug-in +stops DevSound and sends the completion event back to the client via controller +framework.

Playing +a DTMF tone

In this example, a client application wants to play +a Dual-Tone Multi-Frequency (DTMF) tone. The MMF CMdaAudioToneUtility client +API is used to play the DTMF tone. Unlike other MMF APIs, the CMdaAudioToneUtility does +not require a controller plug-in. This is because the input and output of +the API is already in a known data format and does not require encoding or +decoding. The CMdaAudioToneUtility communicates directly +with DevSound.

The main steps in playing the DTMF tone are:

The client application +prepares the CMdaAudioToneUtility to play a DTMF tone.
The client application +asks the CMdaAudioToneUtility to start playing the tone.
The CMdaAudioToneUtility asks +DevSound to play the tone.
The CMdaAudioToneUtility informs +the client application that the playing of the tone is complete.

Playing +an AVI file

In this example, a client application wants to play +an Audio Video Interleaved (AVI) file; output is to a screen and speakers. +The AVI file contains audio and video data, so the CVideoPlayerUtility class +that can manipulate both types of data is used.

The main steps in +playing the AVI file are:

The client application +requests to play an AVI file to the MMF CVideoPlayerUtility class.
The MMF CVideoPlayerUtility +class passes the request to the MMF controller framework. The controller framework +loads the AVI controller
The AVI controller plug-in +initializes the DevSound and DevVideo.
The AVI controller plug-in +reads the data in the AVI file and sends the audio data to DevSound and the +video data to DevVideo.
DevSound outputs the +audio data.
DevVideo sends the video +data to be decoded to the corresponding codec. The decoded video data is then +displayed on the screen.

AVI files support Dolby audio also. The client application requests +for Dolby play back are processed in the similar way.