这一节我们要了解 MediaCodecList 中的信息是如何加载的，以及这些信息是如何使用到的。

// static
sp<IMediaCodecList> MediaCodecList::getLocalInstance() {Mutex::Autolock autoLock(sInitMutex);if (sCodecList == nullptr) {MediaCodecList *codecList = new MediaCodecList(GetBuilders());if (codecList->initCheck() == OK) {sCodecList = codecList;if (isProfilingNeeded()) {ALOGV("Codec profiling needed, will be run in separated thread.");pthread_t profiler;if (pthread_create(&profiler, nullptr, profilerThreadWrapper, nullptr) != 0) {ALOGW("Failed to create thread for codec profiling.");}}} else {// failure to initialize may be temporary. retry on next call.delete codecList;}}return sCodecList;
}sp<IMediaCodecList> MediaCodecList::sRemoteList;sp<MediaCodecList::BinderDeathObserver> MediaCodecList::sBinderDeathObserver;
sp<IBinder> MediaCodecList::sMediaPlayer;  // kept since linked to deathvoid MediaCodecList::BinderDeathObserver::binderDied(const wp<IBinder> &who __unused) {Mutex::Autolock _l(sRemoteInitMutex);sRemoteList.clear();sBinderDeathObserver.clear();
}// static
sp<IMediaCodecList> MediaCodecList::getInstance() {Mutex::Autolock _l(sRemoteInitMutex);if (sRemoteList == nullptr) {sMediaPlayer = defaultServiceManager()->getService(String16("media.player"));sp<IMediaPlayerService> service =interface_cast<IMediaPlayerService>(sMediaPlayer);if (service.get() != nullptr) {sRemoteList = service->getCodecList();if (sRemoteList != nullptr) {sBinderDeathObserver = new BinderDeathObserver();sMediaPlayer->linkToDeath(sBinderDeathObserver.get());}}if (sRemoteList == nullptr) {// if failed to get remote list, create local listsRemoteList = getLocalInstance();}}return sRemoteList;
}MediaCodecList::MediaCodecList(std::vector<MediaCodecListBuilderBase*> builders) {mGlobalSettings = new AMessage();mCodecInfos.clear();MediaCodecListWriter writer;for (MediaCodecListBuilderBase *builder : builders) {if (builder == nullptr) {ALOGD("ignored a null builder");continue;}auto currentCheck = builder->buildMediaCodecList(&writer);if (currentCheck != OK) {ALOGD("ignored failed builder");continue;} else {mInitCheck = currentCheck;}}writer.writeGlobalSettings(mGlobalSettings);writer.writeCodecInfos(&mCodecInfos);std::stable_sort(mCodecInfos.begin(),mCodecInfos.end(),[](const sp<MediaCodecInfo> &info1, const sp<MediaCodecInfo> &info2) {// null is lowestreturn info1 == nullptr|| (info2 != nullptr && info1->getRank() < info2->getRank());});// remove duplicate entriesbool dedupe = property_get_bool("debug.stagefright.dedupe-codecs", true);if (dedupe) {std::set<std::string> codecsSeen;for (auto it = mCodecInfos.begin(); it != mCodecInfos.end(); ) {std::string codecName = (*it)->getCodecName();if (codecsSeen.count(codecName) == 0) {codecsSeen.emplace(codecName);it++;} else {it = mCodecInfos.erase(it);}}}
}MediaCodecList::~MediaCodecList() {
}status_t MediaCodecList::initCheck() const {return mInitCheck;
}