MediaPlayer代码分析(1)-初始化和设置数据的过程

本文分析了android4.4.4的MediaPlayer的初始化和设置数据的过程

{"native_init", "()V", (void *)android_media_MediaPlayer_native_init},

static void android_media_MediaPlayer_native_init(JNIEnv *env)
{jclass clazz;clazz = env->FindClass("android/media/MediaPlayer");if (clazz == NULL) {return;}fields.context = env->GetFieldID(clazz, "mNativeContext", "I");if (fields.context == NULL) {return;}fields.post_event = env->GetStaticMethodID(clazz, "postEventFromNative","(Ljava/lang/Object;IIILjava/lang/Object;)V");if (fields.post_event == NULL) {return;}fields.surface_texture = env->GetFieldID(clazz, "mNativeSurfaceTexture", "I");if (fields.surface_texture == NULL) {return;}clazz = env->FindClass("android/net/ProxyProperties");if (clazz == NULL) {return;}fields.proxyConfigGetHost =env->GetMethodID(clazz, "getHost", "()Ljava/lang/String;");fields.proxyConfigGetPort =env->GetMethodID(clazz, "getPort", "()I");fields.proxyConfigGetExclusionList =env->GetMethodID(clazz, "getExclusionList", "()Ljava/lang/String;");
}

初始化，得到Java层的各种用于jni层的变量，回调函数

{"native_setup", "(Ljava/lang/Object;)V", (void *)android_media_MediaPlayer_native_setup},

static void
android_media_MediaPlayer_native_setup(JNIEnv *env, jobject thiz, jobject weak_this)
{ALOGV("native_setup");sp<MediaPlayer> mp = new MediaPlayer();if (mp == NULL) {jniThrowException(env, "java/lang/RuntimeException", "Out of memory");return;}// create new listener and give it to MediaPlayersp<JNIMediaPlayerListener> listener = new JNIMediaPlayerListener(env, thiz, weak_this);mp->setListener(listener);// Stow our new C++ MediaPlayer in an opaque field in the Java object.setMediaPlayer(env, thiz, mp);
}

mp = new MediaPlayer();

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;

mAudioSessionId = AUdioSystem::newAudioSessionId();，得到新的AudioSessionId

int AudioSystem::newAudioSessionId() {const sp<IAudioFlinger>& af = AudioSystem::get_audio_flinger();if (af == 0) return 0;return af->newAudioSessionId();
}

获取audioflinger的BpBinder
AudioSystem::get_audio_flinger()

const sp<IAudioFlinger>& AudioSystem::get_audio_flinger()
{Mutex::Autolock _l(gLock);if (gAudioFlinger == 0) {sp<IServiceManager> sm = defaultServiceManager();sp<IBinder> binder;do {binder = sm->getService(String16("media.audio_flinger"));if (binder != 0)break;ALOGW("AudioFlinger not published, waiting...");usleep(500000); // 0.5 s} while (true);if (gAudioFlingerClient == NULL) {gAudioFlingerClient = new AudioFlingerClient();} else {if (gAudioErrorCallback) {gAudioErrorCallback(NO_ERROR);}}binder->linkToDeath(gAudioFlingerClient);gAudioFlinger = interface_cast<IAudioFlinger>(binder);gAudioFlinger->registerClient(gAudioFlingerClient);}ALOGE_IF(gAudioFlinger==0, "no AudioFlinger!?");return gAudioFlinger;
}

af->newAUdioSessionId()

int AudioFlinger::newAudioSessionId()
{return nextUniqueId();
}

nextUniqueId()

uint32_t AudioFlinger::nextUniqueId()
{return android_atomic_inc(&mNextUniqueId);
}

每增加一个audiosession，将使用mNextUniqueId记录这个session号，它的声明如下：

volatile int32_t                    mNextUniqueId;

使得访问它的线程都可以获取到，同时使用android_atomic_inc函数，原子增加它，防止竞争，提高了线程安全。volatile只是实现了变量的可见性，不提供原子操作性。

AudioSystem::acquireAudioSessionId(int audioSession)

void AudioSystem::acquireAudioSessionId(int audioSession) {const sp<IAudioFlinger>& af = AudioSystem::get_audio_flinger();if (af != 0) {af->acquireAudioSessionId(audioSession);}
}

af->acquireAudioSessionId(sessionid)

void AudioFlinger::acquireAudioSessionId(int audioSession)
{Mutex::Autolock _l(mLock);pid_t caller = IPCThreadState::self()->getCallingPid();ALOGV("acquiring %d from %d", audioSession, caller);// Ignore requests received from processes not known as notification client. The request// is likely proxied by mediaserver (e.g CameraService) and releaseAudioSessionId() can be// called from a different pid leaving a stale session reference.  Also we don't know how// to clear this reference if the client process dies.if (mNotificationClients.indexOfKey(caller) < 0) {ALOGV("acquireAudioSessionId() unknown client %d for session %d", caller, audioSession);return;}size_t num = mAudioSessionRefs.size();for (size_t i = 0; i< num; i++) {AudioSessionRef *ref = mAudioSessionRefs.editItemAt(i);if (ref->mSessionid == audioSession && ref->mPid == caller) {ref->mCnt++;ALOGV(" incremented refcount to %d", ref->mCnt);return;}}mAudioSessionRefs.push(new AudioSessionRef(audioSession, caller));ALOGV(" added new entry for %d", audioSession);
}

通过audiosessionId，将mediaplayer，audioflinger绑定起来。每个audiosession和一个pid对应，组成了一个AudioSessionRef。AudioSessionRefs队列维护当前系统中运行的audiosession。

mp->setListener()

status_t MediaPlayer::setListener(const sp<MediaPlayerListener>& listener)
{ALOGV("setListener");Mutex::Autolock _l(mLock);mListener = listener;return NO_ERROR;
}

mListener用于MediaPlayer::notify()中，功能是将底层的各种状态，通过它返回到java层。

setMediaPlayer()，对新旧player的引用计数。

static sp<MediaPlayer> setMediaPlayer(JNIEnv* env, jobject thiz, const sp<MediaPlayer>& player)
{Mutex::Autolock l(sLock);sp<MediaPlayer> old = (MediaPlayer*)env->GetIntField(thiz, fields.context);if (player.get()) {player->incStrong((void*)setMediaPlayer);}if (old != 0) {old->decStrong((void*)setMediaPlayer);}env->SetIntField(thiz, fields.context, (int)player.get());return old;
}

SetIntField(thiz, fields.context, (int)player.get())，将创建的player与Java层的mNativeContext联系起来。mNativeContext在Java层的EventHandler.handleMessage中判断是否是对应的底层mediaplayer返回的信息。如果不是，就不处理。

MediaPlayer::setDataSource()

status_t MediaPlayer::setDataSource(const sp<IStreamSource> &source)
{ALOGV("setDataSource");status_t err = UNKNOWN_ERROR;const sp<IMediaPlayerService>& service(getMediaPlayerService());    // 获得BpMediaPlayerService对象if (service != 0) {sp<IMediaPlayer> player(service->create(this, mAudioSessionId)); // 获得BpMediaPlayerif ((NO_ERROR != doSetRetransmitEndpoint(player)) ||(NO_ERROR != player->setDataSource(source))) {player.clear();}err = attachNewPlayer(player);}return err;
}

getMediaPlayerService()

const sp<IMediaPlayerService>&
IMediaDeathNotifier::getMediaPlayerService()
{ALOGV("getMediaPlayerService");Mutex::Autolock _l(sServiceLock);if (sMediaPlayerService == 0) {sp<IServiceManager> sm = defaultServiceManager();sp<IBinder> binder;do {binder = sm->getService(String16("media.player"));if (binder != 0) {break;}ALOGW("Media player service not published, waiting...");usleep(500000); // 0.5 s} while (true);if (sDeathNotifier == NULL) {sDeathNotifier = new DeathNotifier();}binder->linkToDeath(sDeathNotifier);sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);}ALOGE_IF(sMediaPlayerService == 0, "no media player service!?");return sMediaPlayerService;
}

该函数从ServiceManager得到了MediaPlayerPlayerService的Bp端，sMediaPlayerService就是BpMediaPlayerService。

之后对IMediaPlayer player进行赋值。

service->create(this, mAudioSessionId)。create是BpMediaPlayerService里的函数。

    virtual sp<IMediaPlayer> create(const sp<IMediaPlayerClient>& client, int audioSessionId) {Parcel data, reply;data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());data.writeStrongBinder(client->asBinder());data.writeInt32(audioSessionId);remote()->transact(CREATE, data, &reply);return interface_cast<IMediaPlayer>(reply.readStrongBinder());}

该函数向BnMediaPlayerService发送了CREATE请求，请求Bn端创建一个BpMediaPlayer。

经过Binder驱动的调用，现在BnMediaPlayerService接收到了transact发送过来的命令，接着将在Bn端的OnTransact中处理CREATE命令

status_t BnMediaPlayerService::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{switch (code) {case CREATE: {CHECK_INTERFACE(IMediaPlayerService, data, reply);sp<IMediaPlayerClient> client =interface_cast<IMediaPlayerClient>(data.readStrongBinder());int audioSessionId = data.readInt32();sp<IMediaPlayer> player = create(client, audioSessionId);reply->writeStrongBinder(player->asBinder());      // 返回BpMediaPlayerreturn NO_ERROR;} break;

BnMediaPlayerService接收到命令，取得client(IMediaPlayerClient)和audioSessionId后，将调用MediaPlayerService::create函数。

sp<IMediaPlayer> MediaPlayerService::create(const sp<IMediaPlayerClient>& client,int audioSessionId)
{pid_t pid = IPCThreadState::self()->getCallingPid();int32_t connId = android_atomic_inc(&mNextConnId);sp<Client> c = new Client(this, pid, connId, client, audioSessionId,IPCThreadState::self()->getCallingUid());      // 创建一个BnMediaPlayerALOGV("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);}return c;
}

create函数此时将创建BnMediaPlayer，也就是Client类。之后将得到的client经过binder返回给BpMediaPlayer

接着进入player->setDataSource(source)，由于player是BpMediaPlayer，所以需要到BnMediaPlayer里找对应的处理。

    status_t setDataSource(const sp<IStreamSource> &source) {Parcel data, reply;data.writeInterfaceToken(IMediaPlayer::getInterfaceDescriptor());data.writeStrongBinder(source->asBinder());remote()->transact(SET_DATA_SOURCE_STREAM, data, &reply);return reply.readInt32();}

SET_DATA_SOURCE_FD命令在Bn端的处理

case SET_DATA_SOURCE_STREAM: {CHECK_INTERFACE(IMediaPlayer, data, reply);sp<IStreamSource> source =interface_cast<IStreamSource>(data.readStrongBinder());reply->writeInt32(setDataSource(fd, offset, length));return NO_ERROR;}

接着找到setDataSource函数对应的MediaPlayerService文件中的调用

status_t MediaPlayerService::Client::setDataSource(int fd, int64_t offset, int64_t length)
{ALOGV("setDataSource fd=%d, offset=%lld, length=%lld", fd, offset, length);struct stat sb;int ret = fstat(fd, &sb);if (ret != 0) {ALOGE("fstat(%d) failed: %d, %s", fd, ret, strerror(errno));return UNKNOWN_ERROR;}if (offset >= sb.st_size) {ALOGE("offset error");::close(fd);return UNKNOWN_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) {return NO_INIT;}// now set data sourcesetDataSource_post(p, p->setDataSource(fd, offset, length));return mStatus;
}

在这里先暂停分析，先介绍android中自带的几种播放器以及注册过程。

在MediaPlayerService对象创建时，会注册几种系统默认的播放器。

MediaPlayerService::MediaPlayerService()
{ALOGV("MediaPlayerService created");mNextConnId = 1;。。。MediaPlayerFactory::registerBuiltinFactories();
}

registerBuiltinFactories()

void MediaPlayerFactory::registerBuiltinFactories() {Mutex::Autolock lock_(&sLock);if (sInitComplete)return;registerFactory_l(new StagefrightPlayerFactory(), STAGEFRIGHT_PLAYER);registerFactory_l(new NuPlayerFactory(), NU_PLAYER);registerFactory_l(new SonivoxPlayerFactory(), SONIVOX_PLAYER);registerFactory_l(new TestPlayerFactory(), TEST_PLAYER);sInitComplete = true;
}

好了在这里看到了系统默认注册的4个播放器，分别是StagefrightPlayer, NuPlayer, SonivoxPlayer和TestPlayer。

其实系统中定义了播放器类型的枚举

enum player_type {PV_PLAYER = 1,SONIVOX_PLAYER = 2,STAGEFRIGHT_PLAYER = 3,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,
};

由于android在2.3之后不适用opencore架构了，现在使用的是stagefright架构，所以pvplayer代码中已经消失了。

registerFactory_l(IFactory* factory, player_type type)

status_t MediaPlayerFactory::registerFactory_l(IFactory* factory,player_type type) {if (NULL == factory) {ALOGE("Failed to register MediaPlayerFactory of type %d, factory is"" NULL.", type);return BAD_VALUE;}if (sFactoryMap.indexOfKey(type) >= 0) {ALOGE("Failed to register MediaPlayerFactory of type %d, type is"" already registered.", type);return ALREADY_EXISTS;}if (sFactoryMap.add(type, factory) < 0) {ALOGE("Failed to register MediaPlayerFactory of type %d, failed to add"" to map.", type);return UNKNOWN_ERROR;}return OK;
}

向sFactoryMap的键值对中加入对应类型的播放器。

回到setDataSource函数，此时需要得到文件对应的播放器，函数MediaPlayerFactory::getPlayerType其实就是一个宏定义

#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) {                             \ret = getDefaultPlayerType();                   \}                                                   \\return ret;

里面会对每个播放器进行打分，也就是看哪种播放器最合适。这其实是根据文件类型判断的，每种媒体文件都有指示文件格式的字段。
一般都是选择StageFrightPlayer。那么假定player_type是STAGEFRIGHT_PLAYER。

接着进入MediaPlayerService::Client::setDataSource_pre(player_type playerType)

sp<MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre(player_type playerType)
{ALOGV("player type = %d", playerType);// create the right type of playersp<MediaPlayerBase> p = createPlayer(playerType);if (p == NULL) {return p;}if (!p->hardwareOutput()) {mAudioOutput = new AudioOutput(mAudioSessionId, IPCThreadState::self()->getCallingUid());static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);}return p;
}

该函数将创建对应的播放器，并且设置AudioOutput。
createPlayer(player_type)

sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
{// determine if we have the right player typesp<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);}return p;
}

继续看MediaPlayerFactory::createPlayer

sp<MediaPlayerBase> MediaPlayerFactory::createPlayer(player_type playerType,void* cookie,notify_callback_f notifyFunc) {sp<MediaPlayerBase> p;IFactory* factory;status_t init_result;Mutex::Autolock lock_(&sLock);if (sFactoryMap.indexOfKey(playerType) < 0) {ALOGE("Failed to create player object of type %d, no registered"" factory", playerType);return p;}factory = sFactoryMap.valueFor(playerType);CHECK(NULL != factory);p = factory->createPlayer();if (p == NULL) {ALOGE("Failed to create player object of type %d, create failed",playerType);return p;}init_result = p->initCheck();if (init_result == NO_ERROR) {p->setNotifyCallback(cookie, notifyFunc);} else {ALOGE("Failed to create player object of type %d, initCheck failed"" (res = %d)", playerType, init_result);p.clear();}return p;
}

首先检查传入的类型是否有播放器注册，如果没有就报错。有的话会调用播放器创建函数进行创建。

class StagefrightPlayerFactory :public MediaPlayerFactory::IFactory {public:virtual sp<MediaPlayerBase> createPlayer() {ALOGV(" create StagefrightPlayer");return new StagefrightPlayer();}
};

StagefrightPlayer()

StagefrightPlayer::StagefrightPlayer(): mPlayer(new AwesomePlayer) {ALOGV("StagefrightPlayer");mPlayer->setListener(this);
}

至此，我们终于见到了播放器的庐山真面目，原来是AwsomePlayer，帅得兜了好几个圈子。

当看完StagefrightPlayer.cpp后，我们发现，原来这个StagefrightPlayer就是AwsomePlayer封装了一层，里面所有的工作几乎都是AwsomwPlayer去完成的。

那么后面的分析，我们将跳过StagefrightPlayer文件，直接分析AwsomePlayer。

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

先看p->setDataSource()，这其实是调用AwsomePlayer的setDataSource

status_t AwesomePlayer::setDataSource(int fd, int64_t offset, int64_t length) {Mutex::Autolock autoLock(mLock);reset_l();sp<DataSource> dataSource = new FileSource(fd, offset, length);status_t err = dataSource->initCheck();if (err != OK) {return err;}mFileSource = dataSource;{Mutex::Autolock autoLock(mStatsLock);mStats.mFd = fd;mStats.mURI = String8();}return setDataSource_l(dataSource);

AwesomePlayer::setDataSource_l()

status_t AwesomePlayer::setDataSource_l(const sp<DataSource> &dataSource) {sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource);if (extractor == NULL) {return UNKNOWN_ERROR;}if (extractor->getDrmFlag()) {checkDrmStatus(dataSource);}return setDataSource_l(extractor);
}

MediaExtractor::Create(dataSource)

sp<MediaExtractor> MediaExtractor::Create(const sp<DataSource> &source, const char *mime) {sp<AMessage> meta;String8 tmp;if (mime == NULL) {float confidence;if (!source->sniff(&tmp, &confidence, &meta)) {ALOGV("FAILED to autodetect media content.");return NULL;}mime = tmp.string();ALOGV("Autodetected media content as '%s' with confidence %.2f",mime, confidence);}bool isDrm = false;// DRM MIME type syntax is "drm+type+original" where// type is "es_based" or "container_based" and// original is the content's cleartext MIME typeif (!strncmp(mime, "drm+", 4)) {const char *originalMime = strchr(mime+4, '+');if (originalMime == NULL) {// second + not foundreturn NULL;}++originalMime;if (!strncmp(mime, "drm+es_based+", 13)) {// DRMExtractor sets container metadata kKeyIsDRM to 1return new DRMExtractor(source, originalMime);} else if (!strncmp(mime, "drm+container_based+", 20)) {mime = originalMime;isDrm = true;} else {return NULL;}}MediaExtractor *ret = NULL;if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG4)|| !strcasecmp(mime, "audio/mp4")) {ret = new MPEG4Extractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG)) {ret = new MP3Extractor(source, meta);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_NB)|| !strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_WB)) {ret = new AMRExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_FLAC)) {ret = new FLACExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WAV)) {ret = new WAVExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_OGG)) {ret = new OggExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MATROSKA)) {ret = new MatroskaExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2TS)) {ret = new MPEG2TSExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WVM)) {// Return now.  WVExtractor should not have the DrmFlag set in the block below.return new WVMExtractor(source);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AAC_ADTS)) {ret = new AACExtractor(source, meta);} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2PS)) {ret = new MPEG2PSExtractor(source);}if (ret != NULL) {if (isDrm) {ret->setDrmFlag(true);} else {ret->setDrmFlag(false);}}return ret;
}

由于传入的mime是null，所以extractor需要sniff出mime类型。

系统默认注册了几种文件类型

void DataSource::RegisterDefaultSniffers() {Mutex::Autolock autoLock(gSnifferMutex);if (gSniffersRegistered) {return;}RegisterSniffer_l(SniffMPEG4);RegisterSniffer_l(SniffMatroska);RegisterSniffer_l(SniffOgg);RegisterSniffer_l(SniffWAV);RegisterSniffer_l(SniffFLAC);RegisterSniffer_l(SniffAMR);RegisterSniffer_l(SniffMPEG2TS);RegisterSniffer_l(SniffMP3);RegisterSniffer_l(SniffAAC);RegisterSniffer_l(SniffMPEG2PS);RegisterSniffer_l(SniffWVM);char value[PROPERTY_VALUE_MAX];if (property_get("drm.service.enabled", value, NULL)&& (!strcmp(value, "1") || !strcasecmp(value, "true"))) {RegisterSniffer_l(SniffDRM);}gSniffersRegistered = true;
}

sniff函数的流程

bool DataSource::sniff(String8 *mimeType, float *confidence, sp<AMessage> *meta) {*mimeType = "";*confidence = 0.0f;meta->clear();{Mutex::Autolock autoLock(gSnifferMutex);if (!gSniffersRegistered) {return false;}}for (List<SnifferFunc>::iterator it = gSniffers.begin();it != gSniffers.end(); ++it) {String8 newMimeType;float newConfidence;sp<AMessage> newMeta;if ((*it)(this, &newMimeType, &newConfidence, &newMeta)) {if (newConfidence > *confidence) {*mimeType = newMimeType;*confidence = newConfidence;*meta = newMeta;}}}return *confidence > 0.0;
}

待判断出MIMWTYPE后，就会调用对应的提取器XXXExatractor对文件进行提取。

setDataSource_l(extractor)函数做了如下工作：

1 获取文件的bitrate，kKeyBitRate

2 获取视频流

2.1 获取视频宽度，kKeyDisplayWidth

2.2 获取视频高度，kKeyDisplayHeight

3 获取音频流

4 获得视频的字幕

status_t AwesomePlayer::setDataSource_l(const sp<MediaExtractor> &extractor) {// Attempt to approximate overall stream bitrate by summing all// tracks' individual bitrates, if not all of them advertise bitrate,// we have to fail.int64_t totalBitRate = 0;mExtractor = extractor;for (size_t i = 0; i < extractor->countTracks(); ++i) {sp<MetaData> meta = extractor->getTrackMetaData(i);int32_t bitrate;if (!meta->findInt32(kKeyBitRate, &bitrate)) {const char *mime;CHECK(meta->findCString(kKeyMIMEType, &mime));ALOGV("track of type '%s' does not publish bitrate", mime);totalBitRate = -1;break;}totalBitRate += bitrate;}mBitrate = totalBitRate;ALOGV("mBitrate = %lld bits/sec", mBitrate);{Mutex::Autolock autoLock(mStatsLock);mStats.mBitrate = mBitrate;mStats.mTracks.clear();mStats.mAudioTrackIndex = -1;mStats.mVideoTrackIndex = -1;}bool haveAudio = false;bool haveVideo = false;for (size_t i = 0; i < extractor->countTracks(); ++i) {sp<MetaData> meta = extractor->getTrackMetaData(i);const char *_mime;CHECK(meta->findCString(kKeyMIMEType, &_mime));String8 mime = String8(_mime);if (!haveVideo && !strncasecmp(mime.string(), "video/", 6)) {setVideoSource(extractor->getTrack(i));haveVideo = true;// Set the presentation/display sizeint32_t displayWidth, displayHeight;bool success = meta->findInt32(kKeyDisplayWidth, &displayWidth);if (success) {success = meta->findInt32(kKeyDisplayHeight, &displayHeight);}if (success) {mDisplayWidth = displayWidth;mDisplayHeight = displayHeight;}{Mutex::Autolock autoLock(mStatsLock);mStats.mVideoTrackIndex = mStats.mTracks.size();mStats.mTracks.push();TrackStat *stat =&mStats.mTracks.editItemAt(mStats.mVideoTrackIndex);stat->mMIME = mime.string();}} else if (!haveAudio && !strncasecmp(mime.string(), "audio/", 6)) {setAudioSource(extractor->getTrack(i));haveAudio = true;mActiveAudioTrackIndex = i;{Mutex::Autolock autoLock(mStatsLock);mStats.mAudioTrackIndex = mStats.mTracks.size();mStats.mTracks.push();TrackStat *stat =&mStats.mTracks.editItemAt(mStats.mAudioTrackIndex);stat->mMIME = mime.string();}if (!strcasecmp(mime.string(), MEDIA_MIMETYPE_AUDIO_VORBIS)) {// Only do this for vorbis audio, none of the other audio// formats even support this ringtone specific hack and// retrieving the metadata on some extractors may turn out// to be very expensive.sp<MetaData> fileMeta = extractor->getMetaData();int32_t loop;if (fileMeta != NULL&& fileMeta->findInt32(kKeyAutoLoop, &loop) && loop != 0) {modifyFlags(AUTO_LOOPING, SET);}}} else if (!strcasecmp(mime.string(), MEDIA_MIMETYPE_TEXT_3GPP)) {addTextSource_l(i, extractor->getTrack(i));}}if (!haveAudio && !haveVideo) {if (mWVMExtractor != NULL) {return mWVMExtractor->getError();} else {return UNKNOWN_ERROR;}}mExtractorFlags = extractor->flags();return OK;
}

这里主要分析getTrack，给函数主要用于读取音视频的track记录。下面各举一栗子。video的是mpeg4，audio的是amr

video的track

MPEG4Extractor::getTrack

sp<MediaSource> MPEG4Extractor::getTrack(size_t index) {status_t err;if ((err = readMetaData()) != OK) {return NULL;}Track *track = mFirstTrack;while (index > 0) {if (track == NULL) {return NULL;}track = track->next;--index;}if (track == NULL) {return NULL;}ALOGV("getTrack called, pssh: %d", mPssh.size());return new MPEG4Source(track->meta, mDataSource, track->timescale, track->sampleTable,mSidxEntries, mMoofOffset);
}

之后是AwesomePlayer::setVideoSource

void AwesomePlayer::setVideoSource(sp<MediaSource> source) {CHECK(source != NULL);mVideoTrack = source;
}

mVideoTrack在后面用于codec的视频解码用。

audio的track

AMRExtrator::getTrack

sp<MediaSource> AMRExtractor::getTrack(size_t index) {if (mInitCheck != OK || index != 0) {return NULL;}return new AMRSource(mDataSource, mMeta, mIsWide,mOffsetTable, mOffsetTableLength);
}

创建一个AMRSource对象。
之后是AwesomePlayer::setAudioSource

void AwesomePlayer::setAudioSource(sp<MediaSource> source) {CHECK(source != NULL);mAudioTrack = source;
}

mAudioTrack用于之后的codec音频解码用。

最后是setDataSource_post，它返回之前设置的状态

void MediaPlayerService::Client::setDataSource_post(const sp<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;}
}

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