Android Audio 資料流詳解

 Android Audio Architecture 圖如下所示

 

詳細調用路徑如下

1. 音頻播放
範例程式碼
MediaPlayer mp = new MediaPlayer();
mp.setDataSource(PATH_TO_FILE);
mp.prepare();
mp.start();

 

1.1 MediaPlayer mp = new MediaPlayer()

實現流程如下表：

函數名	檔案名稱
MediaPlayer:: MediaPlayer	MediaPlayer.Java
MediaPlayer::native_setup	MediaPlayer.Java
android_media_MediaPlayer_native_setup	android_media_MediaPlayer.cpp
MediaPlayer::MediaPlayer	MediaPlayer.cpp

 

1.2 mp.setDataSource(PATH_TO_FILE);

實現流程如下：

函數名	檔案名稱
MediaPlayer::setDataSource	MediaPlayer.Java
android_media_MediaPlayer_setDataSource	android_media_MediaPlayer.cpp
MediaPlayer::setDataSource	MediaPlayer.cpp
-MediaPlayer::getMediaPlayerService	MediaPlayer.cpp
-IMediaPlayerService	IMediaPlayerService.h
-IMediaPlayerService::create	MediaPlayer.cpp
--MediaPlayerService::create	MediaPlayerService.cpp
-IMediaPlayer::setDataSource	MediaPlayer.cpp
--BpMediaPlayer::setDataSource	IMediaPlayer.cpp
--MediaPlayerService::Client::setDataSource(真正執行操作)	MediaPlayerService.cpp
--android::createPlayer	MediaPlayerService.cpp
-- new StagefrightPlayer	MediaPlayerService.cpp
--new AudioOutput	MediaPlayerService.cpp
--StagefrightPlayer::setDataSource	StagefrightPlayer.cpp
--AwesomePlayer::setDataSource	AwesomePlayer.cpp
--AwesomePlayer::setDataSource_l	AwesomePlayer.cpp

 

1.3 mp.prepare() 

函數名	檔案名稱
MediaPlayer:: prepare	MediaPlayer.Java
android_media_MediaPlayer_prepare	android_media_MediaPlayer.cpp
MediaPlayer:: prepare	MediaPlayer.cpp
MidiFile:: prepare	MidiFile.cpp
VorbisPlayer:: prepare	VorbisPlayer.cpp
VorbisPlayer::createOutputTrack	VorbisPlayer.cpp
AudioOutput::open	MediaPlayerService.cpp
AudioTrack::AudioTrack	AudioTrack.cpp
AudioSystem::get_audio_flinger	AudioSystem.cpp
AudioFlinger::createTrack	AudioFlinger.cpp

 

1.4 mp.start()

函數名	檔案名稱
MediaPlayer:: start	MediaPlayer.Java
android_media_MediaPlayer_start	android_media_MediaPlayer.cpp
MediaPlayer::start	MediaPlayer.cpp
PVPlayer:: start	PVPlayer.h
MidiFile:: start	MidiFile.cpp
VorbisPlayer:: start	VorbisPlayer.cpp
AudioTrack::start	AudioTrack.cpp

MediaPlayerService:: MediaPlayerService(MediaPlayerService.cpp)由systemserver進程建立，在檔案system_init.cpp裡的函數system_init()調用MediaPlayerService::instantiate建立

getPlayerType(MediaPlayerService.cpp)返回3種player:
1) PV_PLAYER:播放mp3
2) SONIVOX_PLAYER:播放midi
3) VORBIS_PLAYER:播放ogg,

 

簡單說來，播放流程如下：
Java端發起調用，MediaPlayer會轉至MediaPlayerService,然後會調用相應的解碼工具解碼後建立AudioTrack，所有待輸出的AudioTrack在AudioFlinger::AudioMixer裡合成，然後通過AudioHAL(AudioHardwareInterface的實際實現者)傳至實際的硬體來實現播放