【stagefrightplayer】1 调用过程

概述

---

android中的多媒体播放结构是：client-server模式

client端对应的类是：MediaPlayer -- framework/base/media/java/android/media/MediaPlayer.java

server端对应的类是：MediaPlayer->MediaPlayerService->Stagefrigthplayer->AwesomePlayer

其中mediaplayerservice是service,MediaPlayer通过binder机制与其交互。

这里Java层的MediaPlayer类与Cpp层的MediaPlayer代码交互不介绍了，自己不了解，只介绍下层的过程。

注：对于mediaplayer类的方法介绍，可参考译文

本篇主要介绍一个典型的播放调用过程

下面是一个典型的播放序列：

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1. MediaPlayer player=new MediaPlayer()
2. player->setDataSource(url,header);
3. player->prepare();
4. player->start();
5. ...

  
  
MediaPlayer player=new MediaPlayer()
player->setDataSource(url,header);
player->prepare();
player->start();
...
  
  

1、构造函数下面就介绍具体的调用流程，起点为MediaPlayer.cpp

---

代码如下

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1. MediaPlayer::MediaPlayer()
2. {
3. ALOGV("constructor");
4. mListener = NULL;
5. mCookie = NULL;
6. mStreamType = AUDIO_STREAM_MUSIC;
7. mCurrentPosition = -1;
8. mSeekPosition = -1;
9. mCurrentState = MEDIA_PLAYER_IDLE;
10. mPrepareSync =false;
11. mPrepareStatus = NO_ERROR;
12. mLoop =false;
13. mLeftVolume = mRightVolume =1.0;
14. mVideoWidth = mVideoHeight =0;
15. mLockThreadId =0;
16. mAudioSessionId = AudioSystem::newAudioSessionId();
17. AudioSystem::acquireAudioSessionId(mAudioSessionId);
18. mSendLevel =0;
19. mRetransmitEndpointValid =false;
20. }

  
  
MediaPlayer::MediaPlayer()
{
ALOGV("constructor");
mListener = NULL;
mCookie = NULL;
mStreamType = AUDIO_STREAM_MUSIC;
mCurrentPosition = -1;
mSeekPosition = -1;
mCurrentState = MEDIA_PLAYER_IDLE;
mPrepareSync =false;
mPrepareStatus = NO_ERROR;
mLoop =false;
mLeftVolume = mRightVolume =1.0;
mVideoWidth = mVideoHeight =0;
mLockThreadId =0;
mAudioSessionId = AudioSystem::newAudioSessionId();
AudioSystem::acquireAudioSessionId(mAudioSessionId);
mSendLevel =0;
mRetransmitEndpointValid =false;
}
  
  

主要是基本的初始化，比较简单。

2、setDataSource

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入口代码如下

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1. status_t MediaPlayer::setDataSource(
2. constchar *url, const KeyedVector<String8, String8> *headers)
3. {
4. ALOGV("setDataSource(%s)", url);
5. status_t err = BAD_VALUE;
6. if(url != NULL) {
7. constsp<IMediaPlayerService>& service(getMediaPlayerService());
8. if(service != 0) {
9. sp<IMediaPlayer> player(service->create(getpid(),this, mAudioSessionId));
10. if((NO_ERROR != doSetRetransmitEndpoint(player)) ||
11. (NO_ERROR != player->setDataSource(url, headers))) {
12. player.clear();
13. }
14. err = attachNewPlayer(player);
15. }
16. }
17. returnerr;
18. }

  
  
status_t MediaPlayer::setDataSource(
constchar *url, const KeyedVector <String8, String8> *headers)
{
ALOGV("setDataSource(%s)", url);
status_t err = BAD_VALUE;
if(url != NULL) {
constsp <IMediaPlayerService>& service(getMediaPlayerService());
if(service != 0) {
sp <IMediaPlayer> player(service->create(getpid(),this, mAudioSessionId));
if((NO_ERROR != doSetRetransmitEndpoint(player)) ||
(NO_ERROR != player->setDataSource(url, headers))) {
player.clear();
}
err = attachNewPlayer(player);
}
}
returnerr;
}
  
  

先看下 service->create(getpid(), this, mAudioSessionId)操作，代码在mediaplayerservice.cpp中 setDataSource的操作就转成通过与mediaplayerservice的交互来完成了

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1. sp<IMediaPlayer> MediaPlayerService::create(pid_t pid,const sp<IMediaPlayerClient>& client,
2. intaudioSessionId)
3. {
4. int32_t connId = android_atomic_inc(&mNextConnId);
6. sp<Client> c =new Client(
7. this, pid, connId, client, audioSessionId,
8. IPCThreadState::self()->getCallingUid());
10. ALOGV("Create new client(%d) from pid %d, uid %d, ", connId, pid,
11. IPCThreadState::self()->getCallingUid());
13. wp<Client> w = c;
14. {
15. Mutex::Autolock lock(mLock);
16. mClients.add(w);
17. }
18. returnc;
19. }

  
  
sp <IMediaPlayer> MediaPlayerService::create(pid_t pid,const sp <IMediaPlayerClient>& client,
intaudioSessionId)
{
int32_t connId = android_atomic_inc(&mNextConnId);

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);
}
returnc;
}
  
  

而且，Client类的继承关系为：Client->BnMediaPlayer->IMediaPlayer分析上面代码，可以看出create方法，是构造了一个Client对象，并且将此client对象添加到mediapalyerservice类的全局列表中：mClient

因此在setDataSource中的

1	sp<IMediaPlayer> player(service->create(getpid(), this , mAudioSessionId));

语句相当于

1	sp<IMediaPlayer> player( new Client(**));

即player最终是用Client对象来初始化，可以直接认为player==client

[说明]c++功力较差，此处可能不严谨

紧接着执行player->setDataSource(url, headers)，即Clients::setDataSource

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1. status_t MediaPlayerService::Client::setDataSource(intfd, int64_t offset, int64_t length)
2. {
3. ALOGV("setDataSource fd=%d, offset=%lld, length=%lld", fd, offset, length);
4. struct stat sb;
5. intret = fstat(fd, &sb);
6. if(ret != 0) {
7. ALOGE("fstat(%d) failed: %d, %s", fd, ret, strerror(errno));
8. returnUNKNOWN_ERROR;
9. }
11. ALOGV("st_dev = %llu", sb.st_dev);
12. ALOGV("st_mode = %u", sb.st_mode);
13. ALOGV("st_uid = %lu", sb.st_uid);
14. ALOGV("st_gid = %lu", sb.st_gid);
15. ALOGV("st_size = %llu", sb.st_size);
17. if(offset >= sb.st_size) {
18. ALOGE("offset error");
19. ::close(fd);
20. returnUNKNOWN_ERROR;
21. }
22. if(offset + length > sb.st_size) {
23. length = sb.st_size - offset;
24. ALOGV("calculated length = %lld", length);
25. }
27. player_type playerType = MediaPlayerFactory::getPlayerType(this,
28. fd,
29. offset,
30. length);
31. sp<MediaPlayerBase> p = setDataSource_pre(playerType);
32. if(p == NULL) {
33. returnNO_INIT;
34. }
36. // now set data source
37. setDataSource_post(p, p->setDataSource(fd, offset, length));
38. returnmStatus;
39. }

  
  
status_t MediaPlayerService::Client::setDataSource(intfd, int64_t offset, int64_t length)
{
ALOGV("setDataSource fd=%d, offset=%lld, length=%lld", fd, offset, length);
struct stat sb;
intret = fstat(fd, &sb);
if(ret != 0) {
ALOGE("fstat(%d) failed: %d, %s", fd, ret, strerror(errno));
returnUNKNOWN_ERROR;
}

ALOGV("st_dev = %llu", sb.st_dev);
ALOGV("st_mode = %u", sb.st_mode);
ALOGV("st_uid = %lu", sb.st_uid);
ALOGV("st_gid = %lu", sb.st_gid);
ALOGV("st_size = %llu", sb.st_size);

if(offset >= sb.st_size) {
ALOGE("offset error");
::close(fd);
returnUNKNOWN_ERROR;
}
if(offset + length > sb.st_size) {
length = sb.st_size - offset;
ALOGV("calculated length = %lld", length);
}

player_type playerType = MediaPlayerFactory::getPlayerType(this,
fd,
offset,
length);
sp <MediaPlayerBase> p = setDataSource_pre(playerType);
if(p == NULL) {
returnNO_INIT;
}

// now set data source
setDataSource_post(p, p->setDataSource(fd, offset, length));
returnmStatus;
}
  
  

2.1 getPlayerType代码比较清晰，首选是选择播放器类型，之后调用setDataSource_pre以及setDataSource_post下面分别来看。

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1. #define GET_PLAYER_TYPE_IMPL(a...) \
2. Mutex::Autolock lock_(&sLock); \
3. \
4. player_type ret = STAGEFRIGHT_PLAYER; \
5. float bestScore =0.0; \
6. \
7. for(size_t i = 0; i < sFactoryMap.size(); ++i) { \
8. \
9. IFactory* v = sFactoryMap.valueAt(i); \
10. float thisScore; \
11. CHECK(v != NULL); \
12. thisScore = v->scoreFactory(a, bestScore); \
13. if(thisScore > bestScore) { \
14. ret = sFactoryMap.keyAt(i); \
15. bestScore = thisScore; \
16. } \
17. } \
18. \
19. if(0.0 == bestScore) { \
20. bestScore = getDefaultPlayerType(); \
21. } \
22. \
23. returnret;
25. player_type MediaPlayerFactory::getPlayerType(constsp<IMediaPlayer>& client,
26. intfd,
27. int64_t offset,
28. int64_t length) {
29. GET_PLAYER_TYPE_IMPL(client, fd, offset, length);
30. }

  
  
#define GET_PLAYER_TYPE_IMPL(a...) \
Mutex::Autolock lock_(&sLock); \
\
player_type ret = STAGEFRIGHT_PLAYER; \
float bestScore =0.0; \
\
for(size_t i = 0; i < sFactoryMap.size(); ++i) { \
\
IFactory* v = sFactoryMap.valueAt(i); \
float thisScore; \
CHECK(v != NULL); \
thisScore = v->scoreFactory(a, bestScore); \
if(thisScore > bestScore) { \
ret = sFactoryMap.keyAt(i); \
bestScore = thisScore; \
} \
} \
\
if(0.0 == bestScore) { \
bestScore = getDefaultPlayerType(); \
} \
\
returnret;

player_type MediaPlayerFactory::getPlayerType(constsp <IMediaPlayer>& client,
intfd,
int64_t offset,
int64_t length) {
GET_PLAYER_TYPE_IMPL(client, fd, offset, length);
}
  
  

这里如果所有播放器都不合适，则选择默认播放器这里流程是，从播放器仓库中选取最佳播放器，通过scoreFactory来确定

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1. player_type MediaPlayerFactory::getDefaultPlayerType() {
2. char value[PROPERTY_VALUE_MAX];
3. if(property_get("media.stagefright.use-nuplayer", value, NULL)
4. && (!strcmp("1", value) || !strcasecmp("true", value))) {
5. returnNU_PLAYER;
6. }
8. returnSTAGEFRIGHT_PLAYER;
9. }

  
  
player_type MediaPlayerFactory::getDefaultPlayerType() {
char value[PROPERTY_VALUE_MAX];
if(property_get("media.stagefright.use-nuplayer", value, NULL)
&& (!strcmp("1", value) || !strcasecmp("true", value))) {
returnNU_PLAYER;
}

returnSTAGEFRIGHT_PLAYER;
}
  
  

这里有几种类型的播放器，会在mediaplayerservice服务类 的构造函数中来注册，代码如下代码中可以看出，一般情况下，STAGEFRIGHT_PLAYER为默认播放器

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1. MediaPlayerService::MediaPlayerService()
2. {
3. ***
4. MediaPlayerFactory::registerBuiltinFactories();
5. }

  
  
MediaPlayerService::MediaPlayerService()
{
***
MediaPlayerFactory::registerBuiltinFactories();
}
  
  

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1. void MediaPlayerFactory::registerBuiltinFactories() {
2. Mutex::Autolock lock_(&sLock);
4. if(sInitComplete)
5. return;
7. registerFactory_l(newStagefrightPlayerFactory(), STAGEFRIGHT_PLAYER);
8. registerFactory_l(newNuPlayerFactory(), NU_PLAYER);
9. registerFactory_l(newSonivoxPlayerFactory(), SONIVOX_PLAYER);
10. registerFactory_l(newTestPlayerFactory(), TEST_PLAYER);
12. sInitComplete =true;
13. }

  
  
void MediaPlayerFactory::registerBuiltinFactories() {
Mutex::Autolock lock_(&sLock);

if(sInitComplete)
return;

registerFactory_l(newStagefrightPlayerFactory(), STAGEFRIGHT_PLAYER);
registerFactory_l(newNuPlayerFactory(), NU_PLAYER);
registerFactory_l(newSonivoxPlayerFactory(), SONIVOX_PLAYER);
registerFactory_l(newTestPlayerFactory(), TEST_PLAYER);

sInitComplete =true;
}
  
  

从registerBuiltinFactories的实现可以看出共注册了四个播放器类型。后面会介绍几个播放器的用途等

下面挑选STAGEFRIGHT_PLAYER类型作为例子看下

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1. class StagefrightPlayerFactory :
2. publicMediaPlayerFactory::IFactory {
3. public:
4. virtual float scoreFactory(constsp<IMediaPlayer>& client,
5. intfd,
6. int64_t offset,
7. int64_t length,
8. float curScore) {
9. char buf[20];
10. lseek(fd, offset, SEEK_SET);
11. read(fd, buf, sizeof(buf));
12. lseek(fd, offset, SEEK_SET);
14. long ident = *((long*)buf);
16. // Ogg vorbis?
17. if(ident == 0x5367674f)// 'OggS'
18. return1.0;
20. return0.0;
21. }
23. virtual sp<MediaPlayerBase> createPlayer() {
24. ALOGV(" create StagefrightPlayer");
25. returnnew StagefrightPlayer();
26. }
27. };

  
  
class StagefrightPlayerFactory :
publicMediaPlayerFactory::IFactory {
public:
virtual float scoreFactory(constsp <IMediaPlayer>& client,
intfd,
int64_t offset,
int64_t length,
float curScore) {
char buf[20];
lseek(fd, offset, SEEK_SET);
read(fd, buf, sizeof(buf));
lseek(fd, offset, SEEK_SET);

long ident = *((long*)buf);

// Ogg vorbis?
if(ident == 0x5367674f)// 'OggS'
return1.0;

return0.0;
}

virtual sp <MediaPlayerBase> createPlayer() {
ALOGV(" create StagefrightPlayer");
returnnew StagefrightPlayer();
}
};
  
  

比较简单，就是一些判断条件，这里还提供了createPlayer，返回实际的播放器对象，后面用的着。

2.2 setDataSource_pre

具体代码如下

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1. sp<MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre(
2. player_type playerType)
3. {
4. ALOGV("player type = %d", playerType);
6. // create the right type of player
7. sp<MediaPlayerBase> p = createPlayer(playerType);
8. if(p == NULL) {
9. returnp;
10. }
12. if(!p->hardwareOutput()) {
13. mAudioOutput =new AudioOutput(mAudioSessionId);
14. static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);
15. }
17. returnp;
18. }

  
  
sp <MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre(
player_type playerType)
{
ALOGV("player type = %d", playerType);

// create the right type of player
sp <MediaPlayerBase> p = createPlayer(playerType);
if(p == NULL) {
returnp;
}

if(!p->hardwareOutput()) {
mAudioOutput =new AudioOutput(mAudioSessionId);
static_cast <MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);
}

returnp;
}
  
  

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1. sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
2. {
3. // determine if we have the right player type
4. sp<MediaPlayerBase> p = mPlayer;
5. if((p != NULL) && (p->playerType() != playerType)) {
6. ALOGV("delete player");
7. p.clear();
8. }
9. if(p == NULL) {
10. p = MediaPlayerFactory::createPlayer(playerType,this, notify);
11. }
13. if(p != NULL) {
14. p->setUID(mUID);
15. }
17. returnp;
18. }

  
  
sp <MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
{
// determine if we have the right player type
sp <MediaPlayerBase> p = mPlayer;
if((p != NULL) && (p->playerType() != playerType)) {
ALOGV("delete player");
p.clear();
}
if(p == NULL) {
p = MediaPlayerFactory::createPlayer(playerType,this, notify);
}

if(p != NULL) {
p->setUID(mUID);
}

returnp;
}
  
  

主要是创建播放器

上面看具体StagefrightPlayerFactory 实现的时候，代码中实现了createPlayer，此处就是调用的此方法

因此等价于return (new StagefrightPlayer()) ;

2.3 setDataSource_post

上面的代码的主要目的是找到对应的播放器，下面主要是执行具体的setdatasource操作

这里需要注意的是 实际的工作是在调用的时候完成的

1	setDataSource_post(p, p->setDataSource(fd, offset, length));

调用的时候，执行了实际播放器的setDataSource方法，而实际的setDataSource_post 仅仅是将播放器保存在本地成员mPlayer中，代码如下

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1. void MediaPlayerService::Client::setDataSource_post(
2. constsp<MediaPlayerBase>& p,
3. status_t status)
4. {
5. ALOGV(" setDataSource");
6. mStatus = status;
7. if(mStatus != OK) {
8. ALOGE(" error: %d", mStatus);
9. return;
10. }
12. // Set the re-transmission endpoint if one was chosen.
13. if(mRetransmitEndpointValid) {
14. mStatus = p->setRetransmitEndpoint(&mRetransmitEndpoint);
15. if(mStatus != NO_ERROR) {
16. ALOGE("setRetransmitEndpoint error: %d", mStatus);
17. }
18. }
20. if(mStatus == OK) {
21. mPlayer = p;
22. }
23. }

  
  
void MediaPlayerService::Client::setDataSource_post(
constsp <MediaPlayerBase>& p,
status_t status)
{
ALOGV(" setDataSource");
mStatus = status;
if(mStatus != OK) {
ALOGE(" error: %d", mStatus);
return;
}

// Set the re-transmission endpoint if one was chosen.
if(mRetransmitEndpointValid) {
mStatus = p->setRetransmitEndpoint(&mRetransmitEndpoint);
if(mStatus != NO_ERROR) {
ALOGE("setRetransmitEndpoint error: %d", mStatus);
}
}

if(mStatus == OK) {
mPlayer = p;
}
}
  
  

下面就进入实际播放器stagefritplayer中看具体实现了（此处以stagefrightplayer为例）

通过上面的介绍，熟悉了如何从MediaPlayer（Java类）一步一步调用到实际工作的类StageFrigtPlayer

这里只是以setDataSource为例，其他方法如prepare等类似。

下面这张图表示了调用流程

总结下几种播放器的区别

StagefrightPlayer： 默认播放器，本地文件基本都使用其播放

NuPlayerDriver：主要用于播放网络视频,http https rtsp等

SonivoxPlayer：用于播放midi等类型的音乐

下一篇着重分析stagefrigtplayer的主要结构