Android 多媒体播放流程

MediaPlayer 框架

§ Android 1.0→Packet video – Open core
§ Android 1.6→Open Core 2.0
§ Android 2.0→Stagefright
§ Android 2.1→Stagefright
§ Android 2.3→Stagefright with enhancements
§ Android 3.0→Stagefright + HLS for first time
§ Android 4.1 to 4.3→SF – Support for MediaCodec
§ Android 5.0→MediaSession and MediaController classes introduced

Android中的MediaPlayer播放框架经历了OpenCore, StageFrightPlayer(AwesomePlayer)，然后NuPlayerDriver。Android2.3 引入流媒体框架，而流媒体框架的核心是NuPlayer。Android4.0之后HttpLive和RTSP协议开始使用NuPlayer播放器，本地播放还是AwesomePlayer， Android5.0（L版本）之后本地播放也开始使用NuPlayer播放器。

m8976/frameworks/av/include/media/MediaPlayerInterface.h
enum player_type {
NU_PLAYER = 4,// Test players are available only in the 'test' and 'eng' builds.
// The shared library with the test player is passed passed as an// argument to the 'test:' url in the setDataSource call.
TEST_PLAYER = 5,
DASH_PLAYER = 6,
};

mediaplayer state diagram

State Diagram:

Nuplayer的创建

app层创建MediaPlayer，有两种方式，

MediaPlayer mediaPlayer = MediaPlayer.create(context, R.raw.sound_file_1);
mediaPlayer.start(); // no need to call prepare(); create() does that for you

Or MediaPlayer mediaPlayer = new MediaPlayer() 例如：

public class MyService extends Service implements MediaPlayer.OnPreparedListener {private static final String ACTION_PLAY = "com.example.action.PLAY";MediaPlayer mMediaPlayer = null;public int onStartCommand(Intent intent, int flags, int startId) {...if (intent.getAction().equals(ACTION_PLAY)) {MediaPlayer mediaPlayer = new MediaPlayer(); // initialize it heremMediaPlayer.setOnPreparedListener(this);mMediaPlayer.prepareAsync(); // prepare async to not block main thread}}/** Called when MediaPlayer is ready */public void onPrepared(MediaPlayer player) {player.start();}
}

播放完成需要release mediaplayer

mediaPlayer.release();
mediaPlayer = null;

对于DRM，MediaPlayer的初始化和设置资源不变，使用DRM时候需要注意下面的步骤：

setOnPreparedListener();
setOnDrmInfoListener();
setDataSource();
prepareAsync();
// ....// If the data source content is protected you receive a call to the onDrmInfo() callback.
onDrmInfo() {prepareDrm();getKeyRequest();provideKeyResponse();
}// When prepareAsync() finishes, you receive a call to the onPrepared() callback.
// If there is a DRM, onDrmInfo() sets it up before executing this callback, so you can start the player.
onPrepared() {start();
}// ...play/pause/resume...
stop();
releaseDrm();

上层app通过new创建MediaPlayer后，然后调用setDataSource(),经过jni最终调用mediapalyer.cpp的setDataSource()，然后执行getMediaPlayerService(),获取MediaPlayerService::Client后创建真正意义上的Player，也就是NuPlayer。
frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp

811  sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
812  {
813      // determine if we have the right player type
814      sp<MediaPlayerBase> p = mPlayer;
815      if ((p != NULL) && (p->playerType() != playerType)) {
816          ALOGV("delete player");
817          p.clear();
818      }
819      if (p == NULL) {
820          p = MediaPlayerFactory::createPlayer(playerType, this, notify, mPid);
821      }
822  
823      if (p != NULL) {
824          p->setUID(mUid);
825      }
826  
827      return p;
828  }

进而由MediaPlayerFactory根据playerType创建对应的player，这里是NuplayerDriver
frameworks/av/media/libmediaplayerservice/MediaPlayerFactory.cpp

 virtual sp<MediaPlayerBase> createPlayer(pid_t pid) {
227          ALOGV(" create NuPlayer");
228          return new NuPlayerDriver(pid);
229      }

NuPlayerDriver是对NuPlayer的封装，继承MediaPlayerInterface接口。通过NuPlayer来实现播放的功能。

59  NuPlayerDriver::NuPlayerDriver(pid_t pid)
60      : mState(STATE_IDLE),
61        mIsAsyncPrepare(false),
62        mAsyncResult(UNKNOWN_ERROR),
63        mSetSurfaceInProgress(false),
64        mDurationUs(-1),
65        mPositionUs(-1),
66        mSeekInProgress(false),
67        mPlayingTimeUs(0),
68        mLooper(new ALooper),
69        mPlayer(new NuPlayer(pid)),
70        mPlayerFlags(0),
71        mAnalyticsItem(NULL),
72        mAtEOS(false),
73        mLooping(false),
74        mAutoLoop(false) {
75      ALOGD("NuPlayerDriver(%p) created, clientPid(%d)", this, pid);
76      mLooper->setName("NuPlayerDriver Looper");
77  
78      // set up an analytics record
79      mAnalyticsItem = new MediaAnalyticsItem(kKeyPlayer);
80      mAnalyticsItem->generateSessionID();
81  
82      mLooper->start(
83              false, /* runOnCallingThread */
84              true,  /* canCallJava */
85              PRIORITY_AUDIO);
86      //mPlayer即NuPlayer，继承于AHandle
87      mLooper->registerHandler(mPlayer);
88  
89      mPlayer->setDriver(this);
90  }

setDataSource

setDataSource方法，这个方法有两个功能：一个是根据文件类型获得相应的player，一个是创建相应文件类型的mediaExtractor,解析媒体文件，记录metadata的主要信息。

//android/frameworks/av/media/libmedia/mediaplayer.cpp194  status_t MediaPlayer::setDataSource(const sp<IDataSource> &source)
195  {
196      ALOGV("setDataSource(IDataSource)");
197      status_t err = UNKNOWN_ERROR;
198      const sp<IMediaPlayerService> service(getMediaPlayerService());
199      if (service != 0) {
200          sp<IMediaPlayer> player(service->create(this, mAudioSessionId));
201          if ((NO_ERROR != doSetRetransmitEndpoint(player)) ||
202              (NO_ERROR != player->setDataSource(source))) {
203              player.clear();
204          }
205          err = attachNewPlayer(player);
206      }
207      return err;
208  }

preparesync

mediaplayer播放的第一步骤setdataSource，下面我们来讲解preparesync的流程，在prepare前我们还有setDisplay这一步，即获取surfacetexture来进行画面的展示
android/frameworks/base/media/java/android/media/MediaPlayer.java

  public static MediaPlayer create(Context context, Uri uri, SurfaceHolder holder,
900              AudioAttributes audioAttributes, int audioSessionId) {
901  
902          try {
903              MediaPlayer mp = new MediaPlayer();
904              final AudioAttributes aa = audioAttributes != null ? audioAttributes :
905                  new AudioAttributes.Builder().build();
906              mp.setAudioAttributes(aa);
907              mp.setAudioSessionId(audioSessionId);
908              mp.setDataSource(context, uri);
909              if (holder != null) {
910                  mp.setDisplay(holder);
911              }
912              mp.prepare();
913              return mp;
914          } catch (IOException ex) {
915              Log.d(TAG, "create failed:", ex);
916              // fall through
917          } catch (IllegalArgumentException ex) {
918              Log.d(TAG, "create failed:", ex);
919              // fall through
920          } catch (SecurityException ex) {
921              Log.d(TAG, "create failed:", ex);
922              // fall through
923          }
924  
925          return null;
926      }public void setDisplay(SurfaceHolder sh) {
750          mSurfaceHolder = sh;
751          Surface surface;
752          if (sh != null) {
753              surface = sh.getSurface();
754          } else {
755              surface = null;
756          }
757          _setVideoSurface(surface);
758          updateSurfaceScreenOn();
759      }

//android/frameworks/base/media/jni/android_media_MediaPlayer.cppstatic void
326  setVideoSurface(JNIEnv *env, jobject thiz, jobject jsurface, jboolean mediaPlayerMustBeAlive)
327  {
328      sp<MediaPlayer> mp = getMediaPlayer(env, thiz);
329      if (mp == NULL) {
330          if (mediaPlayerMustBeAlive) {
331              jniThrowException(env, "java/lang/IllegalStateException", NULL);
332          }
333          return;
334      }
335  
336      decVideoSurfaceRef(env, thiz);
337  
338      sp<IGraphicBufferProducer> new_st;
339      if (jsurface) {
340          sp<Surface> surface(android_view_Surface_getSurface(env, jsurface));
341          if (surface != NULL) {
342              new_st = surface->getIGraphicBufferProducer();
343              if (new_st == NULL) {
344                  jniThrowException(env, "java/lang/IllegalArgumentException",
345                      "The surface does not have a binding SurfaceTexture!");
346                  return;
347              }
348              new_st->incStrong((void*)decVideoSurfaceRef);
349          } else {
350              jniThrowException(env, "java/lang/IllegalArgumentException",
351                      "The surface has been released");
352              return;
353          }
354      }
355  
356      env->SetLongField(thiz, fields.surface_texture, (jlong)new_st.get());
357  
358      // This will fail if the media player has not been initialized yet. This
359      // can be the case if setDisplay() on MediaPlayer.java has been called
360      // before setDataSource(). The redundant call to setVideoSurfaceTexture()
361      // in prepare/prepareAsync covers for this case.
362      mp->setVideoSurfaceTexture(new_st);//setVideoSurfaceTexture
363  }

setVideoSurfaceTexture

//android/frameworks/av/media/libmedia/mediaplayer.cpp244  status_t MediaPlayer::setVideoSurfaceTexture(
245          const sp<IGraphicBufferProducer>& bufferProducer)
246  {
247      ALOGV("setVideoSurfaceTexture");
248      Mutex::Autolock _l(mLock);
249      if (mPlayer == 0) return NO_INIT;
250      return mPlayer->setVideoSurfaceTexture(bufferProducer);
251  }

实际是NuPlayer setVideoSurfaceTextureAsync，这里发送AMessage kWhatSetVideoSurface

375  void NuPlayer::setVideoSurfaceTextureAsync(
376          const sp<IGraphicBufferProducer> &bufferProducer) {
377      sp<AMessage> msg = new AMessage(kWhatSetVideoSurface, this);
378  
379      if (bufferProducer == NULL) {
380          msg->setObject("surface", NULL);
381      } else {
382          msg->setObject("surface", new Surface(bufferProducer, true /* controlledByApp */));
383      }
384  
385      msg->post();
386  }

找到kWhatSetVideoSurface，一直往下在kWhatScanSources时初始化decoder

//android/frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cppcase kWhatScanSources:
975          {
976              int32_t generation;
977              CHECK(msg->findInt32("generation", &generation));
978              if (generation != mScanSourcesGeneration) {
979                  // Drop obsolete msg.
980                  break;
981              }
982  
983              mScanSourcesPending = false;
984  
985              ALOGV("scanning sources haveAudio=%d, haveVideo=%d",
986                   mAudioDecoder != NULL, mVideoDecoder != NULL);
987  
988              bool mHadAnySourcesBefore =
989                  (mAudioDecoder != NULL) || (mVideoDecoder != NULL);
990              bool rescan = false;
991  
992              // initialize video before audio because successful initialization of
993              // video may change deep buffer mode of audio.
994              if (mSurface != NULL) {
995                  if (instantiateDecoder(false, &mVideoDecoder) == -EWOULDBLOCK) {
996                      rescan = true;
997                  }
998              }
999  
1000              // Don't try to re-open audio sink if there's an existing decoder.
1001              if (mAudioSink != NULL && mAudioDecoder == NULL) {
1002                  if (instantiateDecoder(true, &mAudioDecoder) == -EWOULDBLOCK) {
1003                      rescan = true;
1004                  }
1005              }
1006  
1007              if (!mHadAnySourcesBefore
1008                      && (mAudioDecoder != NULL || mVideoDecoder != NULL)) {
1009                  // This is the first time we've found anything playable.
1010  
1011                  if (mSourceFlags & Source::FLAG_DYNAMIC_DURATION) {
1012                      schedulePollDuration();
1013                  }
1014              }
1015  

 status_t NuPlayer::instantiateDecoder(
1779          bool audio, sp<DecoderBase> *decoder, bool checkAudioModeChange) {
1780      // The audio decoder could be cleared by tear down. If still in shut down
1781      // process, no need to create a new audio decoder.
1782      if (*decoder != NULL || (audio && mFlushingAudio == SHUT_DOWN)) {
1783          return OK;
1784      }
1785  
1786      sp<AMessage> format = mSource->getFormat(audio);
1787  
1788      if (format == NULL) {
1789          return UNKNOWN_ERROR;
1790      } else {
1791          status_t err;
1792          if (format->findInt32("err", &err) && err) {
1793              return err;
1794          }
1795      }
1796  
1797      format->setInt32("priority", 0 /* realtime */);
1798  
1799      if (!audio) {
1800          AString mime;
1801          CHECK(format->findString("mime", &mime));
1802  
1803          sp<AMessage> ccNotify = new AMessage(kWhatClosedCaptionNotify, this);
1804          if (mCCDecoder == NULL) {
1805              mCCDecoder = new CCDecoder(ccNotify);
1806          }
1807  
1808          if (mSourceFlags & Source::FLAG_SECURE) {
1809              format->setInt32("secure", true);
1810          }
1811  
1812          if (mSourceFlags & Source::FLAG_PROTECTED) {
1813              format->setInt32("protected", true);
1814          }
1815  
1816          float rate = getFrameRate();
1817          if (rate > 0) {
1818              format->setFloat("operating-rate", rate * mPlaybackSettings.mSpeed);
1819          }
1820      }
1821  
1822      if (audio) {
1823          sp<AMessage> notify = new AMessage(kWhatAudioNotify, this);
1824          ++mAudioDecoderGeneration;
1825          notify->setInt32("generation", mAudioDecoderGeneration);
1826  
1827          if (checkAudioModeChange) {
1828              determineAudioModeChange(format);
1829          }
1830          if (mOffloadAudio) {
1831              mSource->setOffloadAudio(true /* offload */);
1832  
1833              const bool hasVideo = (mSource->getFormat(false /*audio */) != NULL);
1834              format->setInt32("has-video", hasVideo);
1835              *decoder = AVNuFactory::get()->createPassThruDecoder(notify, mSource, mRenderer);
1836              ALOGV("instantiateDecoder audio DecoderPassThrough hasVideo: %d", hasVideo);
1837          } else {
1838              AVNuUtils::get()->setCodecOutputFormat(format);
1839              mSource->setOffloadAudio(false /* offload */);
1840  
1841              *decoder = AVNuFactory::get()->createDecoder(notify, mSource, mPID, mUID, mRenderer);
1842              ALOGV("instantiateDecoder audio Decoder");
1843          }
1844          mAudioDecoderError = false;
1845      } else {
1846          sp<AMessage> notify = new AMessage(kWhatVideoNotify, this);
1847          ++mVideoDecoderGeneration;
1848          notify->setInt32("generation", mVideoDecoderGeneration);
1849  
1850          *decoder = new Decoder(
1851                  notify, mSource, mPID, mUID, mRenderer, mSurface, mCCDecoder);
1852          mVideoDecoderError = false;
1853  
1854          // enable FRC if high-quality AV sync is requested, even if not
1855          // directly queuing to display, as this will even improve textureview
1856          // playback.
1857          {
1858              if (property_get_bool("persist.sys.media.avsync", false)) {
1859                  format->setInt32("auto-frc", 1);
1860              }
1861          }
1862      }
1863      (*decoder)->init();
1864  
1865      // Modular DRM
1866      if (mIsDrmProtected) {
1867          format->setPointer("crypto", mCrypto.get());
1868          ALOGV("instantiateDecoder: mCrypto: %p (%d) isSecure: %d", mCrypto.get(),
1869                  (mCrypto != NULL ? mCrypto->getStrongCount() : 0),
1870                  (mSourceFlags & Source::FLAG_SECURE) != 0);
1871      }
1872  
1873      (*decoder)->configure(format);
1874  
1875      if (!audio) {
1876          sp<AMessage> params = new AMessage();
1877          float rate = getFrameRate();
1878          if (rate > 0) {
1879              params->setFloat("frame-rate-total", rate);
1880          }
1881  
1882          sp<MetaData> fileMeta = getFileMeta();
1883          if (fileMeta != NULL) {
1884              int32_t videoTemporalLayerCount;
1885              if (fileMeta->findInt32(kKeyTemporalLayerCount, &videoTemporalLayerCount)
1886                      && videoTemporalLayerCount > 0) {
1887                  params->setInt32("temporal-layer-count", videoTemporalLayerCount);
1888              }
1889          }
1890  
1891          if (params->countEntries() > 0) {
1892              (*decoder)->setParameters(params);
1893          }
1894      }
1895      return OK;
1896  }// android/frameworks/av/media/libavextensions/mediaplayerservice/AVNuFactory.cpp
62  sp<NuPlayer::DecoderBase> AVNuFactory::createDecoder(
63              const sp<AMessage> &notify,
64              const sp<NuPlayer::Source> &source,
65              pid_t pid,
66              uid_t uid,
67              const sp<NuPlayer::Renderer> &renderer) {
68      return new NuPlayer::Decoder(notify, source, pid, uid, renderer);
69  }

Nuplayer初始化decoder过程中 (*decoder)->configure(format);

289  void NuPlayer::Decoder::onConfigure(const sp<AMessage> &format) {
290      CHECK(mCodec == NULL);
291  
292      mFormatChangePending = false;
293      mTimeChangePending = false;
294  
295      ++mBufferGeneration;
296  
297      AString mime;
298      CHECK(format->findString("mime", &mime));
299  
300      mIsAudio = !strncasecmp("audio/", mime.c_str(), 6);
301      mIsVideoAVC = !strcasecmp(MEDIA_MIMETYPE_VIDEO_AVC, mime.c_str());
302  
303      mComponentName = mime;
304      mComponentName.append(" decoder");
305      ALOGV("[%s] onConfigure (surface=%p)", mComponentName.c_str(), mSurface.get());
306  
307      mCodec = AVUtils::get()->createCustomComponentByName(mCodecLooper, mime.c_str(), false /* encoder */, format);
308      if (mCodec == NULL) {
309      mCodec = MediaCodec::CreateByType(
310              mCodecLooper, mime.c_str(), false /* encoder */, NULL /* err */, mPid, mUid);
311      }
312      int32_t secure = 0;
313      if (format->findInt32("secure", &secure) && secure != 0) {
314          if (mCodec != NULL) {
315              mCodec->getName(&mComponentName);
316              mComponentName.append(".secure");
317              mCodec->release();
318              ALOGI("[%s] creating", mComponentName.c_str());
319              mCodec = MediaCodec::CreateByComponentName(
320                      mCodecLooper, mComponentName.c_str(), NULL /* err */, mPid, mUid);
321          }
322      }

然后创建MediaCodec，Init mediaCodec，initiateAllocateComponent(format);

//android/frameworks/av/media/libstagefright/MediaCodec.cppcase kWhatInit:
1918          {
1919              sp<AReplyToken> replyID;
1920              CHECK(msg->senderAwaitsResponse(&replyID));
1921  
1922              if (mState != UNINITIALIZED) {
1923                  PostReplyWithError(replyID, INVALID_OPERATION);
1924                  break;
1925              }
1926  
1927              mReplyID = replyID;
1928              setState(INITIALIZING);
1929  
1930              AString name;
1931              CHECK(msg->findString("name", &name));
1932  
1933              int32_t nameIsType;
1934              int32_t encoder = false;
1935              CHECK(msg->findInt32("nameIsType", &nameIsType));
1936              if (nameIsType) {
1937                  CHECK(msg->findInt32("encoder", &encoder));
1938              }
1939  
1940              sp<AMessage> format = new AMessage;
1941  
1942              if (nameIsType) {
1943                  format->setString("mime", name.c_str());
1944                  format->setInt32("encoder", encoder);
1945              } else {
1946                  format->setString("componentName", name.c_str());
1947              }
1948  
1949              mCodec->initiateAllocateComponent(format);
1950              break;
1951          }
1952  

MediaCodec调用ACodec的initiateAllocateComponent接口进编解码组件的创建，ACodec就给自己发送了个msg: kWhatAllocateComponent。结合下面的代码来看，这个msg的处理就是单纯的调用执行onAllocateComponent。

android/frameworks/av/media/libstagefright/ACodec.cpp6328  bool ACodec::UninitializedState::onMessageReceived(const sp<AMessage> &msg) {
6329      bool handled = false;
6330  
6331      switch (msg->what()) {
6332          case ACodec::kWhatSetup:
6333          {
6334              onSetup(msg);
6335  
6336              handled = true;
6337              break;
6338          }
6339  
6340          case ACodec::kWhatAllocateComponent:
6341          {
6342              onAllocateComponent(msg);
6343              handled = true;
6344              break;
6345          }

在这里onAllocateComponent，完成omx client连接omx，获取omx bp代理对象，获取matching codecs，allocate node等等

6392  bool ACodec::UninitializedState::onAllocateComponent(const sp<AMessage> &msg) {
6393      ALOGV("onAllocateComponent");
6394  
6395      CHECK(mCodec->mOMXNode == NULL);
6396  
6397      OMXClient client;
6398      bool trebleFlag;
6399      if (client.connect(&trebleFlag) != OK) { //omx client连接omx
6400          mCodec->signalError(OMX_ErrorUndefined, NO_INIT);
6401          return false;
6402      }
6403      mCodec->setTrebleFlag(trebleFlag);
6404  
6405      sp<IOMX> omx = client.interface();//获取omx bp代理对象
6406  
6407      sp<AMessage> notify = new AMessage(kWhatOMXDied, mCodec);
6408  
6409      Vector<AString> matchingCodecs;
6410  
6411      AString mime;
6412  
6413      AString componentName;
6414      int32_t encoder = false;
6415      if (msg->findString("componentName", &componentName)) {
6416          sp<IMediaCodecList> list = MediaCodecList::getInstance();
6417          if (list != NULL && list->findCodecByName(componentName.c_str()) >= 0) {
6418              matchingCodecs.add(componentName);
6419          }
6420          //make sure if the component name contains qcom/qti, we add it to matchingCodecs
6421          //as these components are not present in media_codecs.xml and MediaCodecList won't find
6422          //these component by findCodecByName
6423          if (matchingCodecs.size() == 0 && (componentName.find("qcom", 0) > 0 ||
6424              componentName.find("qti", 0) > 0)) {
6425              matchingCodecs.add(componentName);
6426          }
6427  
6428      } else {
6429          CHECK(msg->findString("mime", &mime));
6430  
6431          if (!msg->findInt32("encoder", &encoder)) {
6432              encoder = false;
6433          }
6434          //findMatchingCodecs
6435          MediaCodecList::findMatchingCodecs(
6436                  mime.c_str(),
6437                  encoder, // createEncoder
6438                  0,       // flags
6439                  &matchingCodecs);
6440      }
6441  
6442      sp<CodecObserver> observer = new CodecObserver;
6443      sp<IOMXNode> omxNode;
6444  
6445      status_t err = NAME_NOT_FOUND;
6446      for (size_t matchIndex = 0; matchIndex < matchingCodecs.size();
6447              ++matchIndex) {
6448          componentName = matchingCodecs[matchIndex];
6449  
6450          pid_t tid = gettid();
6451          int prevPriority = androidGetThreadPriority(tid);
6452          androidSetThreadPriority(tid, ANDROID_PRIORITY_FOREGROUND);
6453          err = omx->allocateNode(componentName.c_str(), observer, &omxNode);//allocate Node
6454          androidSetThreadPriority(tid, prevPriority);
6455  
6456          if (err == OK) {
6457              break;
6458          } else {
6459              ALOGW("Allocating component '%s' failed, try next one.", componentName.c_str());
6460          }
6461  
6462          omxNode = NULL;
6463      }
6464  
6465      if (omxNode == NULL) {
6466          if (!mime.empty()) {
6467              ALOGE("Unable to instantiate a %scoder for type '%s' with err %#x.",
6468                      encoder ? "en" : "de", mime.c_str(), err);
6469          } else {
6470              ALOGE("Unable to instantiate codec '%s' with err %#x.", componentName.c_str(), err);
6471          }
6472  
6473          mCodec->signalError((OMX_ERRORTYPE)err, makeNoSideEffectStatus(err));
6474          return false;
6475      }
6476  
6477      mDeathNotifier = new DeathNotifier(notify);
6478      if (mCodec->getTrebleFlag()) {
6479          auto tOmxNode = omxNode->getHalInterface();
6480          if (!tOmxNode->linkToDeath(mDeathNotifier, 0)) {
6481              mDeathNotifier.clear();
6482          }
6483      } else {
6484          if (IInterface::asBinder(omxNode)->linkToDeath(mDeathNotifier) != OK) {
6485              // This was a local binder, if it dies so do we, we won't care
6486              // about any notifications in the afterlife.
6487              mDeathNotifier.clear();
6488          }
6489      }
6490  
6491      notify = new AMessage(kWhatOMXMessageList, mCodec);
6492      notify->setInt32("generation", ++mCodec->mNodeGeneration);
6493      observer->setNotificationMessage(notify);
6494  
6495      mCodec->mComponentName = componentName;
6496      mCodec->mRenderTracker.setComponentName(componentName);
6497      mCodec->mFlags = 0;
6498  
6499      if (componentName.endsWith(".secure")) {
6500          mCodec->mFlags |= kFlagIsSecure;
6501          mCodec->mFlags |= kFlagIsGrallocUsageProtected;
6502          mCodec->mFlags |= kFlagPushBlankBuffersToNativeWindowOnShutdown;
6503      }
6504  
6505      mCodec->mOMX = omx;
6506      mCodec->mOMXNode = omxNode;
6507      mCodec->mCallback->onComponentAllocated(mCodec->mComponentName.c_str());
6508      mCodec->changeState(mCodec->mLoadedState);
6509  
6510      return true;
6511  }

为什么用surfaceTexture不用surface来展示呢？ICS之前都用的是surfaceview来展示video或者openGL的内容，surfacaview render在surface上，textureview render在surfaceTexture，textureview和surfaceview 这两者有什么区别呢？surfaceview跟应用的视窗不是同一个视窗，它自己new了一个window来展示openGL或者video的内容，这样做有一个好处就是不用重绘应用的视窗，本身就可以不停的更新，但这也带来一些局限性，surfaceview不是依附在应用视窗中，也就不能移动、缩放、旋转，应用ListView或者 ScrollView就比较费劲。Textureview就很好的解决了这些问题。它拥有surfaceview的一切特性外，它也拥有view的一切行为，可以当个view使用。

获取完surfaceTexture，我们就可以prepare/prepareAsync了
prepare是个同步的过程，所以要加锁，prepareAsync_l后缀加_l就是表面是同步的过程。

1 /*
2 **
3 ** Copyright 2006, The Android Open Source Project
4 **
5 ** Licensed under the Apache License, Version 2.0 (the "License");
6 ** you may not use this file except in compliance with the License.
7 ** You may obtain a copy of the License at
8 **
9 **     http://www.apache.org/licenses/LICENSE-2.0
10 **
11 ** Unless required by applicable law or agreed to in writing, software
12 ** distributed under the License is distributed on an "AS IS" BASIS,
13 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 ** See the License for the specific language governing permissions and
15 ** limitations under the License.
16 */
17 
18 //#define LOG_NDEBUG 0
19 #define LOG_TAG "MediaPlayerNative"
20 
21 #include <fcntl.h>
22 #include <inttypes.h>
23 #include <sys/stat.h>
24 #include <sys/types.h>
25 #include <unistd.h>
26 
27 #include <utils/Log.h>
28 
29 #include <binder/IServiceManager.h>
30 #include <binder/IPCThreadState.h>
31 
32 #include <gui/Surface.h>
33 
34 #include <media/mediaplayer.h>
35 #include <media/AudioResamplerPublic.h>
36 #include <media/AudioSystem.h>
37 #include <media/AVSyncSettings.h>
38 #include <media/IDataSource.h>
39 #include <media/MediaAnalyticsItem.h>
40 
41 #include <binder/MemoryBase.h>
42 
43 #include <utils/KeyedVector.h>
44 #include <utils/String8.h>
45 
46 #include <system/audio.h>
47 #include <system/window.h>
48 
49 #ifdef MM_VIDEOSHOT
50 #include <MyosMediaplayer.h>
51 #endif
52 namespace android {
53 
54 MediaPlayer::MediaPlayer()
55 {
56     ALOGV("constructor");
57     mListener = NULL;
58     mCookie = NULL;
59     mStreamType = AUDIO_STREAM_MUSIC;
60     mAudioAttributesParcel = NULL;
61     mCurrentPosition = -1;
62     mCurrentSeekMode = MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC;
63     mSeekPosition = -1;
64     mSeekMode = MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC;
65     mCurrentState = MEDIA_PLAYER_IDLE;
66     mPrepareSync = false;
67     mPrepareStatus = NO_ERROR;
68     mLoop = false;
69     mLeftVolume = mRightVolume = 1.0;
70     mVideoWidth = mVideoHeight = 0;
71     mLockThreadId = 0;
72     mAudioSessionId = (audio_session_t) AudioSystem::newAudioUniqueId(AUDIO_UNIQUE_ID_USE_SESSION);
73     AudioSystem::acquireAudioSessionId(mAudioSessionId, -1);
74     mSendLevel = 0;
75     mRetransmitEndpointValid = false;
76 }
77 
78 MediaPlayer::~MediaPlayer()
79 {
80     ALOGV("destructor");
81     if (mAudioAttributesParcel != NULL) {
82         delete mAudioAttributesParcel;
83         mAudioAttributesParcel = NULL;
84     }
85     AudioSystem::releaseAudioSessionId(mAudioSessionId, -1);
86     disconnect();
87     IPCThreadState::self()->flushCommands();
88 }
89 
90 void MediaPlayer::disconnect()
91 {
92     ALOGV("disconnect");
93     sp<IMediaPlayer> p;
94     {
95         Mutex::Autolock _l(mLock);
96         p = mPlayer;
97         mPlayer.clear();
98     }
99 
100     if (p != 0) {
101         p->disconnect();
102     }
103 }
104 
105 // always call with lock held
106 void MediaPlayer::clear_l()
107 {
108     mCurrentPosition = -1;
109     mCurrentSeekMode = MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC;
110     mSeekPosition = -1;
111     mSeekMode = MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC;
112     mVideoWidth = mVideoHeight = 0;
113     mRetransmitEndpointValid = false;
114 }
115 
116 status_t MediaPlayer::setListener(const sp<MediaPlayerListener>& listener)
117 {
118     ALOGV("setListener");
119     Mutex::Autolock _l(mLock);
120     mListener = listener;
121     return NO_ERROR;
122 }
123 
124 
125 status_t MediaPlayer::attachNewPlayer(const sp<IMediaPlayer>& player)
126 {
127     status_t err = UNKNOWN_ERROR;
128     sp<IMediaPlayer> p;
129     { // scope for the lock
130         Mutex::Autolock _l(mLock);
131 
132         if ( !( (mCurrentState & MEDIA_PLAYER_IDLE) ||
133                 (mCurrentState == MEDIA_PLAYER_STATE_ERROR ) ) ) {
134             ALOGE("attachNewPlayer called in state %d", mCurrentState);
135             return INVALID_OPERATION;
136         }
137 
138         clear_l();
139         p = mPlayer;
140         mPlayer = player;
141         if (player != 0) {
142             mCurrentState = MEDIA_PLAYER_INITIALIZED;
143             player->getDefaultBufferingSettings(&mCurrentBufferingSettings);
144             err = NO_ERROR;
145         } else {
146             mCurrentBufferingSettings = BufferingSettings();
147             ALOGE("Unable to create media player");
148         }
149     }
150 
151     if (p != 0) {
152         p->disconnect();
153     }
154 
155     return err;
156 }
157 
158 status_t MediaPlayer::setDataSource(
159         const sp<IMediaHTTPService> &httpService,
160         const char *url, const KeyedVector<String8, String8> *headers)
161 {
162     ALOGV("setDataSource(%s)", url);
163     status_t err = BAD_VALUE;
164     if (url != NULL) {
165         const sp<IMediaPlayerService> service(getMediaPlayerService());
166         if (service != 0) {
167             sp<IMediaPlayer> player(service->create(this, mAudioSessionId));
168             if ((NO_ERROR != doSetRetransmitEndpoint(player)) ||
169                 (NO_ERROR != player->setDataSource(httpService, url, headers))) {
170                 player.clear();
171             }
172             err = attachNewPlayer(player);
173         }
174     }
175     return err;
176 }
177 
178 status_t MediaPlayer::setDataSource(int fd, int64_t offset, int64_t length)
179 {
180     ALOGV("setDataSource(%d, %" PRId64 ", %" PRId64 ")", fd, offset, length);
181     status_t err = UNKNOWN_ERROR;
182     const sp<IMediaPlayerService> service(getMediaPlayerService());
183     if (service != 0) {
184         sp<IMediaPlayer> player(service->create(this, mAudioSessionId));
185         if ((NO_ERROR != doSetRetransmitEndpoint(player)) ||
186             (NO_ERROR != player->setDataSource(fd, offset, length))) {
187             player.clear();
188         }
189         err = attachNewPlayer(player);
190     }
191     return err;
192 }
193 
194 status_t MediaPlayer::setDataSource(const sp<IDataSource> &source)
195 {
196     ALOGV("setDataSource(IDataSource)");
197     status_t err = UNKNOWN_ERROR;
198     const sp<IMediaPlayerService> service(getMediaPlayerService());
199     if (service != 0) {
200         sp<IMediaPlayer> player(service->create(this, mAudioSessionId));
201         if ((NO_ERROR != doSetRetransmitEndpoint(player)) ||
202             (NO_ERROR != player->setDataSource(source))) {
203             player.clear();
204         }
205         err = attachNewPlayer(player);
206     }
207     return err;
208 }
209 
210 status_t MediaPlayer::invoke(const Parcel& request, Parcel *reply)
211 {
212     Mutex::Autolock _l(mLock);
213     const bool hasBeenInitialized =
214             (mCurrentState != MEDIA_PLAYER_STATE_ERROR) &&
215             ((mCurrentState & MEDIA_PLAYER_IDLE) != MEDIA_PLAYER_IDLE);
216     if ((mPlayer != NULL) && hasBeenInitialized) {
217         ALOGV("invoke %zu", request.dataSize());
218         return  mPlayer->invoke(request, reply);
219     }
220     ALOGE("invoke failed: wrong state %X, mPlayer(%p)", mCurrentState, mPlayer.get());
221     return INVALID_OPERATION;
222 }
223 
224 status_t MediaPlayer::setMetadataFilter(const Parcel& filter)
225 {
226     ALOGD("setMetadataFilter");
227     Mutex::Autolock lock(mLock);
228     if (mPlayer == NULL) {
229         return NO_INIT;
230     }
231     return mPlayer->setMetadataFilter(filter);
232 }
233 
234 status_t MediaPlayer::getMetadata(bool update_only, bool apply_filter, Parcel *metadata)
235 {
236     ALOGD("getMetadata");
237     Mutex::Autolock lock(mLock);
238     if (mPlayer == NULL) {
239         return NO_INIT;
240     }
241     return mPlayer->getMetadata(update_only, apply_filter, metadata);
242 }
243 
244 status_t MediaPlayer::setVideoSurfaceTexture(
245         const sp<IGraphicBufferProducer>& bufferProducer)
246 {
247     ALOGV("setVideoSurfaceTexture");
248     Mutex::Autolock _l(mLock);
249     if (mPlayer == 0) return NO_INIT;
250     return mPlayer->setVideoSurfaceTexture(bufferProducer);
251 }
252 
253 status_t MediaPlayer::getDefaultBufferingSettings(BufferingSettings* buffering /* nonnull */)
254 {
255     ALOGV("getDefaultBufferingSettings");
256 
257     Mutex::Autolock _l(mLock);
258     if (mPlayer == 0) {
259         return NO_INIT;
260     }
261     return mPlayer->getDefaultBufferingSettings(buffering);
262 }
263 
264 status_t MediaPlayer::getBufferingSettings(BufferingSettings* buffering /* nonnull */)
265 {
266     ALOGV("getBufferingSettings");
267 
268     Mutex::Autolock _l(mLock);
269     if (mPlayer == 0) {
270         return NO_INIT;
271     }
272     *buffering = mCurrentBufferingSettings;
273     return NO_ERROR;
274 }
275 
276 status_t MediaPlayer::setBufferingSettings(const BufferingSettings& buffering)
277 {
278     ALOGV("setBufferingSettings");
279 
280     Mutex::Autolock _l(mLock);
281     if (mPlayer == 0) {
282         return NO_INIT;
283      }
284      status_t err =  mPlayer->setBufferingSettings(buffering);
285      if (err == NO_ERROR) {
286          mCurrentBufferingSettings = buffering;
287      }
288      return err;
289  }
290  
291  // must call with lock held
292  status_t MediaPlayer::prepareAsync_l()
293  {
294      if ( (mPlayer != 0) && ( mCurrentState & (MEDIA_PLAYER_INITIALIZED | MEDIA_PLAYER_STOPPED) ) ) {
295          if (mAudioAttributesParcel != NULL) {
296              mPlayer->setParameter(KEY_PARAMETER_AUDIO_ATTRIBUTES, *mAudioAttributesParcel);
297          } else {
298              mPlayer->setAudioStreamType(mStreamType);
299          }
300          mCurrentState = MEDIA_PLAYER_PREPARING;
301          return mPlayer->prepareAsync();
302      }
303      ALOGE("prepareAsync called in state %d, mPlayer(%p)", mCurrentState, mPlayer.get());
304      return INVALID_OPERATION;
305  }

实际是NuplayerDriver

264  status_t NuPlayerDriver::prepare() {
265      ALOGV("prepare(%p)", this);
266      Mutex::Autolock autoLock(mLock);
267      return prepare_l();
268  }
269  
270  status_t NuPlayerDriver::prepare_l() {
271      switch (mState) {
272          case STATE_UNPREPARED:
273              mState = STATE_PREPARING;
274  
275              // Make sure we're not posting any notifications, success or
276              // failure information is only communicated through our result
277              // code.
278              mIsAsyncPrepare = false;
279              mPlayer->prepareAsync();
280              while (mState == STATE_PREPARING) {
281                  mCondition.wait(mLock);
282              }
283              return (mState == STATE_PREPARED) ? OK : UNKNOWN_ERROR;
284          case STATE_STOPPED:
285              // this is really just paused. handle as seek to start
286              mAtEOS = false;
287              mState = STATE_STOPPED_AND_PREPARING;
288              mIsAsyncPrepare = false;
289              mPlayer->seekToAsync(0, MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC /* mode */,
290                      true /* needNotify */);
291              while (mState == STATE_STOPPED_AND_PREPARING) {
292                  mCondition.wait(mLock);
293              }
294              return (mState == STATE_STOPPED_AND_PREPARED) ? OK : UNKNOWN_ERROR;
295          default:
296              return INVALID_OPERATION;
297      };
298  }
299  
300  status_t NuPlayerDriver::prepareAsync() {
301      ALOGV("prepareAsync(%p)", this);
302      Mutex::Autolock autoLock(mLock);
303  
304      switch (mState) {
305          case STATE_UNPREPARED:
306              mState = STATE_PREPARING;
307              mIsAsyncPrepare = true;
308              mPlayer->prepareAsync();
309              return OK;
310          case STATE_STOPPED:
311              // this is really just paused. handle as seek to start
312              mAtEOS = false;
313              mState = STATE_STOPPED_AND_PREPARING;
314              mIsAsyncPrepare = true;
315              mPlayer->seekToAsync(0, MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC /* mode */,
316                      true /* needNotify */);
317              return OK;
318          default:
319              return INVALID_OPERATION;
320      };
321  }

353  void NuPlayer::GenericSource::onPrepareAsync() {} else {
379              if (property_get_bool("media.stagefright.extractremote", true) &&
380                      !FileSource::requiresDrm(mFd, mOffset, mLength, nullptr /* mime */)) {
381                  sp<IBinder> binder =
382                          defaultServiceManager()->getService(String16("media.extractor"));
383                  if (binder != nullptr) {
384                      ALOGD("FileSource remote");
385                      sp<IMediaExtractorService> mediaExService(
386                              interface_cast<IMediaExtractorService>(binder));
387                      sp<IDataSource> source =
388                              mediaExService->makeIDataSource(mFd, mOffset, mLength);
389                      ALOGV("IDataSource(FileSource): %p %d %lld %lld",
390                              source.get(), mFd, (long long)mOffset, (long long)mLength);
391                      if (source.get() != nullptr) {
392                          mDataSource = DataSource::CreateFromIDataSource(source);
393                          if (mDataSource != nullptr) {
394                              // Close the local file descriptor as it is not needed anymore.
395                              close(mFd);
396                              mFd = -1;
397                          }
398                      } else {
399                          ALOGW("extractor service cannot make data source");
400                      }
401                  } else {
402                      ALOGW("extractor service not running");
403                  }
404              }......
430      // init extractor from data source
431      status_t err = initFromDataSource();

//android/frameworks/av/media/libmediaplayerservice/nuplayer/GenericSource.cpp159  status_t NuPlayer::GenericSource::initFromDataSource() {
160      sp<IMediaExtractor> extractor;
161      CHECK(mDataSource != NULL);
162  
163      extractor = MediaExtractor::Create(mDataSource, NULL,
164                  mIsStreaming ? 0 : AVNuUtils::get()->getFlags());
165  
166      if (extractor == NULL) {
167          ALOGE("initFromDataSource, cannot create extractor!");
168          return UNKNOWN_ERROR;
169      }
170  
171      mFileMeta = extractor->getMetaData();

prepare主要目的了，根据类型找到解码器并初始化对应的解码器

OnStart and Decoder

总的来说mediaplayer播放的第一步骤setdataSource，在prepare前我们还有setDisplay这一步，即获取surfacetexture来进行画面的展示。
setDataSource方法，根据文件类型获得相应的player。然后在prepare前initdecoder，创建MediaCodec，完成了prepare前的必要步骤，并且setVideoSurfaceTexture，接着prepare，创建相应文件类型的mediaExtractor，完成Start play前的所有准备工作
在Onstart命令开始后开始decoder，显示