涉及相关文件：
\frameworks\av\media\mediaserver\mediaserver.rc
\frameworks\av\media\mediaserver\main_mediaserver.cpp
\frameworks\av\media\libmediaplayerservice\MediaPlayerService.h
\frameworks\av\media\libmediaplayerservice\MediaPlayerService.cpp
\frameworks\av\media\libmediaplayerservice\MediaPlayerFactory.h
\frameworks\av\media\libmediaplayerservice\MediaPlayerFactory.cpp
\frameworks\av\include\media\IMediaPlayerService.h
\frameworks\av\media\libmedia\include\media\IMediaPlayer.h
MediaPlayerService服务相关类关系图如下：
在\frameworks\av\media\mediaserver\中，mediaserver.rc文件内容如下，启动/system/bin/mediaserver作为media服务
service media /system/bin/mediaserver
class main
user media
group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
ioprio rt 4
writepid /dev/cpuset/foreground/tasks /dev/stune/foreground/tasks
main_mediaserver.cpp中main函数内容如下，获取IServiceManager服务管理对象，然后初始化MediaPlayerService、ResourceManagerService并且将这两个服务加入到ServiceManager中管理。
int main(int argc __unused, char **argv __unused)
{
signal(SIGPIPE, SIG_IGN);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm(defaultServiceManager());
ALOGI("ServiceManager: %p", sm.get());
InitializeIcuOrDie();
MediaPlayerService::instantiate();
ResourceManagerService::instantiate();
registerExtensions();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
MediaPlayerService中的初始化方法如下：
void MediaPlayerService::instantiate() {
defaultServiceManager()->addService(
String16("media.player"), new MediaPlayerService()); //将该服务加入到ServiceManager中
}
MediaPlayerService::MediaPlayerService()
{
ALOGV("MediaPlayerService created");
mNextConnId = 1;
MediaPlayerFactory::registerBuiltinFactories(); //完成player工厂的注册
}
在MediaPlayerFactory.cpp注册了两个工厂类：NuPlayerFactory和TestPlayerFactory（一般debug版本才会用到），注册完成会将两个Ifactory对象加入到容器tFactoryMap中
void MediaPlayerFactory::registerBuiltinFactories() {
Mutex::Autolock lock_(&sLock);
if (sInitComplete)
return;
IFactory* factory = new NuPlayerFactory();
if (registerFactory_l(factory, NU_PLAYER) != OK) //注册将其加入到容器中
delete factory;
factory = new TestPlayerFactory();
if (registerFactory_l(factory, TEST_PLAYER) != OK)
delete factory;
sInitComplete = true;
}
typedef KeyedVector<player_type, IFactory*> tFactoryMap;
NuPlayerFactory实现如下：
class NuPlayerFactory : public MediaPlayerFactory::IFactory {
public:
virtual float scoreFactory(const sp<IMediaPlayer>& /*client*/,
const char* url,
float curScore) {
static const float kOurScore = 0.8;
if (kOurScore <= curScore)
return 0.0;
if (!strncasecmp("http://", url, 7)
|| !strncasecmp("https://", url, 8)
|| !strncasecmp("file://", url, 7)) {
size_t len = strlen(url);
if (len >= 5 && !strcasecmp(".m3u8", &url[len - 5])) {
return kOurScore;
}
if (strstr(url,"m3u8")) {
return kOurScore;
}
if ((len >= 4 && !strcasecmp(".sdp", &url[len - 4])) || strstr(url, ".sdp?")) {
return kOurScore;
}
}
if (!strncasecmp("rtsp://", url, 7)) {
return kOurScore;
}
return 0.0;
}
virtual float scoreFactory(const sp<IMediaPlayer>& /*client*/,
const sp<IStreamSource>& /*source*/,
float /*curScore*/) {
return 1.0;
}
virtual float scoreFactory(const sp<IMediaPlayer>& /*client*/,
const sp<DataSource>& /*source*/,
float /*curScore*/) {
// Only NuPlayer supports setting a DataSource source directly.
return 1.0;
}
virtual sp<MediaPlayerBase> createPlayer(pid_t pid) {
ALOGV(" create NuPlayer");
return new NuPlayerDriver(pid);
}
};
MediaPlayerService中Client对象创建过程如下：
sp<IMediaPlayer> MediaPlayerService::create(const sp<IMediaPlayerClient>& client,
audio_session_t audioSessionId)
{
pid_t pid = IPCThreadState::self()->getCallingPid();
int32_t connId = android_atomic_inc(&mNextConnId);
//新建client对象
sp<Client> c = new Client(
this, pid, connId, client, audioSessionId,
IPCThreadState::self()->getCallingUid());
ALOGV("Create new client(%d) from pid %d, uid %d, ", connId, pid,
IPCThreadState::self()->getCallingUid());
wp<Client> w = c;
{
Mutex::Autolock lock(mLock);
mClients.add(w); //将新创建的client对象加入到容器mClient中
}
return c;
}
client类定义如下，包含了所有针对音视频播放所需要的操作，与native层的MediaPlayer类方法正好对应
class Client : public BnMediaPlayer {
// IMediaPlayer interface
virtual void disconnect();
virtual status_t setVideoSurfaceTexture(
const sp<IGraphicBufferProducer>& bufferProducer);
virtual status_t setBufferingSettings(const BufferingSettings& buffering) override;
virtual status_t getBufferingSettings(
BufferingSettings* buffering /* nonnull */) override;
virtual status_t prepareAsync();
virtual status_t start();
virtual status_t stop();
virtual status_t pause();
virtual status_t isPlaying(bool* state);
//......省略
其中父类定义如下
class BnMediaPlayer: public BnInterface<IMediaPlayer>
{
public:
virtual status_t onTransact( uint32_t code,
const Parcel& data,
Parcel* reply,
uint32_t flags = 0);
};
class IMediaPlayer: public IInterface
{
public:
DECLARE_META_INTERFACE(MediaPlayer);
virtual void disconnect() = 0;
virtual status_t setDataSource(
const sp<IMediaHTTPService> &httpService,
const char *url,
const KeyedVector<String8, String8>* headers) = 0;
virtual status_t setDataSource(int fd, int64_t offset, int64_t length) = 0;
virtual status_t setDataSource(const sp<IStreamSource>& source) = 0;
virtual status_t setDataSource(const sp<IDataSource>& source) = 0;
virtual status_t setVideoSurfaceTexture(
const sp<IGraphicBufferProducer>& bufferProducer) = 0;
virtual status_t getBufferingSettings(
BufferingSettings* buffering /* nonnull */) = 0;
virtual status_t setBufferingSettings(const BufferingSettings& buffering) = 0;
virtual status_t prepareAsync() = 0;
virtual status_t start() = 0;
virtual status_t stop() = 0;
virtual status_t pause() = 0;
virtual status_t isPlaying(bool* state) = 0;
virtual status_t setPlaybackSettings(const AudioPlaybackRate& rate) = 0;
virtual status_t getPlaybackSettings(AudioPlaybackRate* rate /* nonnull */) = 0;
//......省略
MediaPlayerService本身不负责音视频的具体操作，通过管理client接口与工厂类，将具体播放工作通过binder交由其他进程负责完成，而MediaPlayer又是通过binder获取到MediaPlayerService服务，通过发送和接收命令来完成音视频的播放和状态的更新获取等。
![Android MediaPlayer 框架UML图[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)