一文搞懂Codec2解码组件
目录
- 1 前言
- 2 组件的创建
- 3 组件接口
- 4 组件运行原理
- 5 小结
1 前言
在本篇中,我们将关注Codec 2.0以下几个问题:
1.从顶而下,一个解码组件是如何创建的
2.组件的接口有哪些,分别是什么含义
3.组件是如何运行的,输入与输出的数据流是怎样的
2 组件的创建
CCodec在allocate中,通过CreateComponentByName创建了具体的解码组件。
//android/frameworks/av/media/codec2/sfplguin/CCodec.cpp void CCodec::allocate(const sp<MediaCodecInfo> &codecInfo) { ... AString componentName = codecInfo->getCodecName(); std::shared_ptr<Codec2Client> client; // set up preferred component store to access vendor store parameters //从CCodec调用到component是通过HAL层服务的,默认谷歌的原生服务为 //android.hardware.media.c2@IComponentStore/software,默认厂商的服务为 //android.hardware.media.c2@IComponentStore/default,在android小机shell中通过lshal|grep media可以查询 //到正在运行的codec2服务,如果厂商已支持codec2,则可以查询到default服务。如果CCodec中能够创建到default //服务,则可以将该服务设置为Preferred Codec2 ComponentStore,也就是将其作为目标组件。 client = Codec2Client::CreateFromService("default"); if (client) { ALOGI("setting up '%s' as default (vendor) store", client->getServiceName().c_str()); SetPreferredCodec2ComponentStore( std::make_shared<Codec2ClientInterfaceWrapper>(client)); } //创建具体的解码组件或者编码组件,譬如c2.android.avc.decoder //所有omx与codec2的编解码组件支持列表可以在libstagefright/data目录下的xml中查询得到,它们的加载与 //排序情况可以在libstagefright/MediaCodecList.cpp中追踪 std::shared_ptr<Codec2Client::Component> comp = Codec2Client::CreateComponentByName( componentName.c_str(), mClientListener, &client); ... ALOGI("Created component [%s]", componentName.c_str()); mChannel->setComponent(comp); auto setAllocated = [this, comp, client] { Mutexed<State>::Locked state(mState); if (state->get() != ALLOCATING) { state->set(RELEASED); return UNKNOWN_ERROR; } state->set(ALLOCATED); state->comp = comp; mClient = client; return OK; }; ... // initialize config here in case setParameters is called prior to configure Mutexed<Config>::Locked config(mConfig); status_t err = config->initialize(mClient, comp); ... config->queryConfiguration(comp); mCallback->onComponentAllocated(componentName.c_str()); }
继续追踪Codec2Client::CreateComponentByName接口。
//android/frameworks/av/media/codec2/hidl/client/client.cpp std::shared_ptr<Codec2Client::Component> Codec2Client::CreateComponentByName( const char* componentName, const std::shared_ptr<Listener>& listener, std::shared_ptr<Codec2Client>* owner, size_t numberOfAttempts) { std::string key{"create:"}; key.append(componentName); std::shared_ptr<Component> component; c2_status_t status = ForAllServices( key, numberOfAttempts, [owner, &component, componentName, &listener]( const std::shared_ptr<Codec2Client> &client) -> c2_status_t { //调用Codec2Client类的createComponent接口,获取component c2_status_t status = client->createComponent(componentName, listener, &component); ... return status; }); ... return component; }
追踪Codec2Client类的createComponent接口。
\\av\media\codec2\hidl\client\client.cpp c2_status_t Codec2Client::createComponent( const C2String& name, const std::shared_ptr<Codec2Client::Listener>& listener, std::shared_ptr<Codec2Client::Component>* const component) { c2_status_t status; sp<Component::HidlListener> hidlListener = new Component::HidlListener{}; hidlListener->base = listener; //这里的mBase是什么?这里调用的是IComponentStore的createComponent接口 Return<void> transStatus = mBase->createComponent( name, hidlListener, ClientManager::getInstance(), [&status, component, hidlListener]( Status s, const sp<IComponent>& c) { status = static_cast<c2_status_t>(s); if (status != C2_OK) { return; } *component = std::make_shared<Codec2Client::Component>(c); hidlListener->component = *component; }); ... return status; }
我们先看一下IComponentStore的createComponent接口。
\\av\media\codec2\hidl\1.0\utils\include\codec2\hidl\1.0\ComponentStore.h struct ComponentStore : public IComponentStore { ComponentStore(const std::shared_ptr<C2ComponentStore>& store); virtual ~ComponentStore() = default; // Methods from ::android::hardware::media::c2::V1_0::IComponentStore. virtual Return<void> createComponent( const hidl_string& name, const sp<IComponentListener>& listener, const sp<IClientManager>& pool, createComponent_cb _hidl_cb) override; virtual Return<void> createInterface( const hidl_string& name, createInterface_cb _hidl_cb) override;、 ... }
该接口的实现为:
\\av\media\codec2\hidl\1.0\utils\ComponentStore.cpp // Methods from ::android::hardware::media::c2::V1_0::IComponentStore Return<void> ComponentStore::createComponent( const hidl_string& name, const sp<IComponentListener>& listener, const sp<IClientManager>& pool, createComponent_cb _hidl_cb) { sp<Component> component; std::shared_ptr<C2Component> c2component; //C2PlatformComponentStore的createComponent调用 //调用C2PlatformComponentStore的createComponent接口,返回的是一个C2Component对象 //譬如,这个对象可以是C2SoftAvcDec Component对象,也可以是VendorHwAvcDec Component对象 Status status = static_cast<Status>( mStore->createComponent(name, &c2component)); if (status == Status::OK) { onInterfaceLoaded(c2component->intf()); //把前面创建的C2SoftAvcDec“装载”到Component类中,Client调用Component //Component内部会调用到C2SoftAvcDec //Component相当于对原生编解码组件/厂商编解码组件的统一封装 component = new Component(c2component, listener, this, pool); if (!component) { status = Status::CORRUPTED; } else { reportComponentBirth(component.get()); if (component->status() != C2_OK) { status = static_cast<Status>(component->status()); } else { component->initListener(component); if (component->status() != C2_OK) { status = static_cast<Status>(component->status()); } } } } _hidl_cb(status, component); return Void(); }
关于C2PlatformComponentStore的createComponent调用,它的实现在C2Store.cpp中,它继承于C2ComponentStore类,有几个重要成员对象,ComponentModule,ComponentLoader,有几个重要的接口,listComponents(),createComponent(),createInterface()。ComponentLoader包含ComponentModule对象,而ComponentModule主要提供两个接口,createComponent()与createInterface(),内部也包含着C2ComponentFactory成员以及它的创建与销毁接口,分别是C2ComponentFactory::CreateCodec2FactoryFunc,C2ComponentFactory::DestroyCodec2FactoryFunc。
\\av\media\codec2\vndk\C2Store.cpp class C2PlatformComponentStore : public C2ComponentStore { public: virtual std::vector<std::shared_ptr<const C2Component::Traits>> listComponents() override; ... virtual c2_status_t createInterface( C2String name, std::shared_ptr<C2ComponentInterface> *const interface) override; virtual c2_status_t createComponent( C2String name, std::shared_ptr<C2Component> *const component) override; virtual ~C2PlatformComponentStore() override = default; private: /** * An object encapsulating a loaded component module. */ struct ComponentModule : public C2ComponentFactory, public std::enable_shared_from_this<ComponentModule> { virtual c2_status_t createComponent( c2_node_id_t id, std::shared_ptr<C2Component> *component, ComponentDeleter deleter = std::default_delete<C2Component>()) override; virtual c2_status_t createInterface( c2_node_id_t id, std::shared_ptr<C2ComponentInterface> *interface, InterfaceDeleter deleter = std::default_delete<C2ComponentInterface>()) override; ... protected: ... void *mLibHandle; ///< loaded library handle C2ComponentFactory::CreateCodec2FactoryFunc createFactory; ///< loaded create function C2ComponentFactory::DestroyCodec2FactoryFunc destroyFactory; ///< loaded destroy function C2ComponentFactory *mComponentFactory; ///< loaded/created component factory }; /** * An object encapsulating a loadable component module. */ struct ComponentLoader { /** * Load the component module. * * This method simply returns the component module if it is already currently loaded, or * attempts to load it if it is not. */ c2_status_t fetchModule(std::shared_ptr<ComponentModule> *module) { c2_status_t res = C2_OK; std::lock_guard<std::mutex> lock(mMutex); std::shared_ptr<ComponentModule> localModule = mModule.lock(); if (localModule == nullptr) { localModule = std::make_shared<ComponentModule>(); res = localModule->init(mLibPath); if (res == C2_OK) { mModule = localModule; } } *module = localModule; return res; } /** * Creates a component loader for a specific library path (or name). */ ComponentLoader(std::string libPath) : mLibPath(libPath) {} private: std::weak_ptr<ComponentModule> mModule; ///< weak reference to the loaded module }; struct Interface : public C2InterfaceHelper { ... }; /** * Retrieves the component module for a component. */ c2_status_t findComponent(C2String name, std::shared_ptr<ComponentModule> *module); /** * Loads each component module and discover its contents. */ void visitComponents(); std::map<C2String, ComponentLoader> mComponents; ///< path -> component module std::map<C2String, C2String> mComponentNameToPath; ///< name -> path std::vector<std::shared_ptr<const C2Component::Traits>> mComponentList; ... };
C2PlatformComponentStore::createComponent调用findComponent(name, &module)找到拥有component的ComponentModule,再通过module->createComponent(0, component)调用,找到相应的component。
\\av\media\codec2\vndk\C2Store.cpp c2_status_t C2PlatformComponentStore::createComponent( C2String name, std::shared_ptr<C2Component> *const component) { // This method SHALL return within 100ms. component->reset(); std::shared_ptr<ComponentModule> module; c2_status_t res = findComponent(name, &module); if (res == C2_OK) { // TODO: get a unique node ID res = module->createComponent(0, component); } return res; }
findComponent(name, &module)有两步,先通过visitComponents()列举出所有可用的components,再调用ComponentLoader的fetchModule(),找到拥有component的ComponentModule。module可以看作是组件,加载某个module,也就是加载对应的组件,module提供的 createComponent()接口就是用来创建具体component的,譬如C2SoftAvcDec。
\\av\media\codec2\vndk\C2Store.cpp c2_status_t C2PlatformComponentStore::findComponent( C2String name, std::shared_ptr<ComponentModule> *module) { (*module).reset(); visitComponents(); auto pos = mComponentNameToPath.find(name); if (pos != mComponentNameToPath.end()) { return mComponents.at(pos->second).fetchModule(module); } return C2_NOT_FOUND; }
visitComponents()访问mComponents对象(这是一个map对象,将path与component module映射关联,这一映射工作在C2PlatformComponentStore初始化时进行),遍历所有的mComponents,即pathAndLoader对象,如果一个对象的loader能够加载成功,则添加到mComponentNameToPath对象中。
\\av\media\codec2\vndk\C2Store.cpp void C2PlatformComponentStore::visitComponents() { std::lock_guard<std::mutex> lock(mMutex); if (mVisited) { return; } //参考定义 std::map<C2String, ComponentLoader> mComponents; ///< path -> component module for (auto &pathAndLoader : mComponents) { const C2String &path = pathAndLoader.first; ComponentLoader &loader = pathAndLoader.second; std::shared_ptr<ComponentModule> module; if (loader.fetchModule(&module) == C2_OK) { std::shared_ptr<const C2Component::Traits> traits = module->getTraits(); if (traits) { mComponentList.push_back(traits); mComponentNameToPath.emplace(traits->name, path); for (const C2String &alias : traits->aliases) { mComponentNameToPath.emplace(alias, path); } } } } mVisited = true; }
loader.fetchModule(&module)这个函数定义在ComponentLoader类中,在这里再贴一次代码。
\\av\media\codec2\vndk\C2Store.cpp c2_status_t fetchModule(std::shared_ptr<ComponentModule> *module) { c2_status_t res = C2_OK; std::lock_guard<std::mutex> lock(mMutex); std::shared_ptr<ComponentModule> localModule = mModule.lock(); if (localModule == nullptr) { localModule = std::make_shared<ComponentModule>(); res = localModule->init(mLibPath); if (res == C2_OK) { mModule = localModule; } } *module = localModule; return res; }
对于module,会调用初始化函数,初始化成功就算是fetch到了。初始化作了什么工作,参见C2PlatformComponentStore::ComponentModule::init函数,也就是对编解码库dlopen成功,可获得相应的函数地址,譬如,C2SoftAvcDec.cpp中的C2ComponentFactory* CreateCodec2Factory()与void DestroyCodec2Factory()。当然还有其他,不面面俱道了。
\\av\media\codec2\vndk\C2Store.cpp c2_status_t C2PlatformComponentStore::ComponentModule::init( std::string libPath) { ALOGV("in %s", __func__); ALOGV("loading dll"); mLibHandle = dlopen(libPath.c_str(), RTLD_NOW|RTLD_NODELETE); createFactory = (C2ComponentFactory::CreateCodec2FactoryFunc)dlsym(mLibHandle, "CreateCodec2Factory"); LOG_ALWAYS_FATAL_IF(createFactory == nullptr, "createFactory is null in %s", libPath.c_str()); destroyFactory = (C2ComponentFactory::DestroyCodec2FactoryFunc)dlsym(mLibHandle, "DestroyCodec2Factory"); LOG_ALWAYS_FATAL_IF(destroyFactory == nullptr, "destroyFactory is null in %s", libPath.c_str()); mComponentFactory = createFactory(); ... std::shared_ptr<C2ComponentInterface> intf; c2_status_t res = createInterface(0, &intf); ... return mInit; }
那么问题来了,为什么谷歌对它自己的codec2插件组C2PlatformComponentStore设计得这么复杂,能不能简化一点。
3 组件接口
在codec2/components目录下,有base, avc, aom, hevc, aac等文件夹,base目录下是SimpleC2Component.cpp与SimpleC2Interface.cpp以及对应的头文件,avc目录下是C2SoftAvcDec.cpp,C2SoftAvcEnc.cpp以及对应的头文件,其他编解码器文件夹亦同样道理。C2SoftAvcDec,C2SoftHevcDec等编解码器类都是继承于SimpleC2Component类的,也就是说,SimpleC2Component是components的顶层类,它对接了component类的接口,实现了编解码器的公共流程部分,C2SoftAvcDec,C2SoftHevcDec等子类继承SimpleC2Component的一些接口,实现各自的编解码操作。
SimpleC2Component实现的component的接口如下:
\\av\media\codec2\components\base\include\SimpleC2Component.h // C2Component // From C2Component //设置回调 virtual c2_status_t setListener_vb( const std::shared_ptr<Listener> &listener, c2_blocking_t mayBlock) override; //送数据到component,数据打包成某种对象,叫C2Work,这个对象很关键,它包含input与output virtual c2_status_t queue_nb(std::list<std::unique_ptr<C2Work>>* const items) override; //暂时没有多大用处,不管它 virtual c2_status_t announce_nb(const std::vector<C2WorkOutline> &items) override; //跳播使用,将当前数据冲刷掉 virtual c2_status_t flush_sm( flush_mode_t mode, std::list<std::unique_ptr<C2Work>>* const flushedWork) override; //渲染可用的帧 virtual c2_status_t drain_nb(drain_mode_t mode) override; virtual c2_status_t start() override; virtual c2_status_t stop() override; virtual c2_status_t reset() override; virtual c2_status_t release() override; virtual std::shared_ptr<C2ComponentInterface> intf() override; 而C2SoftAvcDec,C2SoftHevcDec等子类继承SimpleC2Component的接口如下: \\av\media\codec2\components\base\include\SimpleC2Component.h virtual c2_status_t onInit() = 0; virtual c2_status_t onStop() = 0; virtual void onReset() = 0; virtual void onRelease() = 0; virtual c2_status_t onFlush_sm() = 0; //最重要的处理函数,处理的对象是C2Work,它包含着输入输出,交互配置方面的类。 virtual void process( const std::unique_ptr<C2Work> &work, const std::shared_ptr<C2BlockPool> &pool) = 0; virtual c2_status_t drain( uint32_t drainMode, const std::shared_ptr<C2BlockPool> &pool) = 0;
4 组件运行原理
SimpleC2Component有一个成员对象WorkHandler,这个类继承于AHandler,也就是说,SimpleC2Component内部运行一个线程,来自上层的接口调用,都可以发送消息到onMessageReceived中排队处理,譬如初始化、停止、重置、释放以及数据处理等工作,都在队列中排队处理,相应的处理都是调用到子类的实现,譬如,onInit(),onStop(),onReset(),onRelease(),以及processQueue()。
我们可以看一下onMessageReceived的实现。
\\av\media\codec2\components\base\SimpleC2Component.cpp void SimpleC2Component::WorkHandler::onMessageReceived(const sp<AMessage> &msg) { std::shared_ptr<SimpleC2Component> thiz = mThiz.lock(); ... switch (msg->what()) { case kWhatProcess: { if (mRunning) { if (thiz->processQueue()) { (new AMessage(kWhatProcess, this))->post(); } } else { ALOGV("Ignore process message as we're not running"); } break; } case kWhatInit: { int32_t err = thiz->onInit(); Reply(msg, &err); [[fallthrough]]; } case kWhatStart: { mRunning = true; break; } case kWhatStop: { int32_t err = thiz->onStop(); Reply(msg, &err); break; } case kWhatReset: { thiz->onReset(); mRunning = false; Reply(msg); break; } case kWhatRelease: { thiz->onRelease(); mRunning = false; Reply(msg); break; } default: { ALOGD("Unrecognized msg: %d", msg->what()); break; } } }
我们看一下AVC解码器内部是如何处理输入与输出数据的,在这个process中,处理完输入,解码,处理输出,在处理output buffer时,process的思路是这样的:从内存池申请一个GraphicBlock,对应地设置给解码器Buffer地址以供解码输出,如果解码后有帧输出,则将当前的GraphicBlock转换为C2Buffer对象,返回给上层。类似于FFMPEG,你给它一个output frame,它就将解码图片填充到frame,你取走显示。可以推断,软解码器内部应该也有申请一个队列的buffer,这个队列维护着解码所需要的参考图像。
\\av\media\codec2\components\avc\C2SoftAvcDec.cpp //省略了部分不影响理解主要流程的代码 void C2SoftAvcDec::process( const std::unique_ptr<C2Work> &work, const std::shared_ptr<C2BlockPool> &pool) { // Initialize output work work->result = C2_OK; work->workletsProcessed = 0u; work->worklets.front()->output.flags = work->input.flags; size_t inOffset = 0u; size_t inSize = 0u; uint32_t workIndex = work->input.ordinal.frameIndex.peeku() & 0xFFFFFFFF; C2ReadView rView = mDummyReadView; if (!work->input.buffers.empty()) { //为了得到输入数据,层层访问,真正放数据的地址在rView.data()[]中 //把work这个对象用思维导图画出来,我们可以更容易的理解work,到底拥有哪些成员,如何访问 rView = work->input.buffers[0]->data().linearBlocks().front().map().get(); inSize = rView.capacity(); ... } bool eos = ((work->input.flags & C2FrameData::FLAG_END_OF_STREAM) != 0); bool hasPicture = false; ALOGV("in buffer attr. size %zu timestamp %d frameindex %d, flags %x", inSize, (int)work->input.ordinal.timestamp.peeku(), (int)work->input.ordinal.frameIndex.peeku(), work->input.flags); size_t inPos = 0; while (inPos < inSize) { //ensureDecoderState会从内存池中fetch一个GraphicBlock //实质上也就是调用Gralloc接口取得一个output buffer if (C2_OK != ensureDecoderState(pool)) { mSignalledError = true; work->workletsProcessed = 1u; work->result = C2_CORRUPTED; return; } ivd_video_decode_ip_t s_decode_ip; ivd_video_decode_op_t s_decode_op; { //mOutBlock即是上述fetch到的output buffer,通过map映射可以得到一个wView,类似于rView //wView.data()[]指向out buffer的真正地址 //wView.data()[C2PlanarLayout::PLANE_Y]就是要存在Y变量的地址 //wView.data()[C2PlanarLayout::PLANE_U]就是要存在U变量的地址 C2GraphicView wView = mOutBlock->map().get(); ... //setDecodeArgs所作的主要工作是,告诉解码器,输入数据的地址是什么,输出地址包括Y/U/V //分量的地址是什么,输入数据的长度是多少 if (!setDecodeArgs(&s_decode_ip, &s_decode_op, &rView, &wView, inOffset + inPos, inSize - inPos, workIndex)) { mSignalledError = true; work->workletsProcessed = 1u; work->result = C2_CORRUPTED; return; } if (false == mHeaderDecoded) { /* Decode header and get dimensions */ setParams(mStride, IVD_DECODE_HEADER); } //解码器库是用了第三方的,已经被谷歌收购 (void) ivdec_api_function(mDecHandle, &s_decode_ip, &s_decode_op); } if (s_decode_op.i4_reorder_depth >= 0 && mOutputDelay != s_decode_op.i4_reorder_depth) { //目前不清楚把这个重排序长度告诉上层有什么作用,TODO mOutputDelay = s_decode_op.i4_reorder_depth; ALOGV("New Output delay %d ", mOutputDelay); C2PortActualDelayTuning::output outputDelay(mOutputDelay); std::vector<std::unique_ptr<C2SettingResult>> failures; c2_status_t err = mIntf->config({&outputDelay}, C2_MAY_BLOCK, &failures); if (err == OK) { work->worklets.front()->output.configUpdate.push_back( C2Param::Copy(outputDelay)); } continue; } if (0 < s_decode_op.u4_pic_wd && 0 < s_decode_op.u4_pic_ht) { if (mHeaderDecoded == false) { mHeaderDecoded = true; setParams(ALIGN64(s_decode_op.u4_pic_wd), IVD_DECODE_FRAME); } if (s_decode_op.u4_pic_wd != mWidth || s_decode_op.u4_pic_ht != mHeight) { mWidth = s_decode_op.u4_pic_wd; mHeight = s_decode_op.u4_pic_ht; CHECK_EQ(0u, s_decode_op.u4_output_present); C2StreamPictureSizeInfo::output size(0u, mWidth, mHeight); std::vector<std::unique_ptr<C2SettingResult>> failures; c2_status_t err = mIntf->config({&size}, C2_MAY_BLOCK, &failures); if (err == OK) { work->worklets.front()->output.configUpdate.push_back( C2Param::Copy(size)); } continue; } } (void)getVuiParams(); hasPicture |= (1 == s_decode_op.u4_frame_decoded_flag); if (s_decode_op.u4_output_present) { //通过createGraphicBuffer调用,将mOutBlock"转换"成C2Buffer对象 //把C2Buffer添加到work对象的输出队列中 //通过listener->onWorkDone_nb回调,可以将work返回到CCodec层 //以上是这个函数以及其内部调用的主要实现内容,内部调用的finish()函数属于SimpleC2Component finishWork(s_decode_op.u4_ts, work); } inPos += s_decode_op.u4_num_bytes_consumed; } if (eos) { drainInternal(DRAIN_COMPONENT_WITH_EOS, pool, work); mSignalledOutputEos = true; } else if (!hasPicture) { fillEmptyWork(work); } work->input.buffers.clear(); }
在Component中,输入与输出对象都封装在work对象中,甚至上下层的配置交互对象也包括在work对象中,与OMX是不一样的,OMX的数据对象是BufferHeader,输入是一个Input BufferHeader,输出是一个Output BufferHeader,对象中包括buffer地址,分配的buffer大小,有效数据长度,有效数据长度的偏移量,buffer标志等。 那么,work对象也应该会包括类似的成员。
我们来看两张思维导图,全局观察work对象。
C2SoftAvcDec::process中有一句代码,从work中访问rView。
rView = work->input.buffers[0]->data().linearBlocks().front().map().get();
从上述两图中,我们可以追踪这一条访问线路,访问C2Work对象的成员C2FrameData,继续访问C2FrameData对外的成员vector linearBlocks(),C2ConstLinearBlock有一个方法C2Acquirable map(),这个映射方法返回一个C2ReadView对象,这个C2ReadView对象有一个data()[]数组,指向了Y/U/V的向量地址,也就是真正存放解码数据的内存地址。而Input与Output都是以C2FrameData来描述,Output并非像Input一样,直接作为C2Work的成员,而是作为C2Work->worklets的成员。worklet是一个list类型,C2SoftAvcDec在存放output buffer的时候,总是存放在第一个worklets的output中,参见思维导图,output是C2FrameData类型,它拥有一个C2Buffer容器,C2SoftAvcDec总是将新的output buffer丢进容器中,它可以一次丢很多个output buffer,然后一次性通过work回送到上层,上层可以一次性从work中取到多个output buffer去作渲染。C2WorkOrdinalStruct ordinal包括着buffer的pts与frameIndex信息。这里有个疑问待解决,为什么output buffer总是存放在第一个worklets的output中,worklets作为一个队列对象,有什么其他的意义?
上面我们分析了两个点,一个是模块的消息处理机制,另一个是如何送数据到解码器再取出帧数据回送到上层,接下来看第三点,CCodec每次送多少输入数据下来,component每次处理多少数据,回送输出数据给CCodec作渲染在哪些地方。
上层是调用SimpleC2Component::queue_nb接口送数据下来的。
\\av\media\codec2\components\base\SimpleC2Component.cpp c2_status_t SimpleC2Component::queue_nb(std::list<std::unique_ptr<C2Work>> * const items) { { Mutexed<ExecState>::Locked state(mExecState); if (state->mState != RUNNING) { return C2_BAD_STATE; } } bool queueWasEmpty = false; { Mutexed<WorkQueue>::Locked queue(mWorkQueue); queueWasEmpty = queue->empty(); while (!items->empty()) { queue->push_back(std::move(items->front())); items->pop_front(); } } if (queueWasEmpty) { (new AMessage(WorkHandler::kWhatProcess, mHandler))->post(); } return C2_OK; }
观察上面的代码,入参是一个列表对象,也就是说,每次送多个work,一个work可以包括一个C2Buffer容器,码流都是放在容器的第一个元素,虽然一个容器可以放多个C2Buffer,但它就只放了一个C2Buffer。我们可以从下面的代码中发现,每一次的process,都只从work中取一个C2Buffer。
\\av\media\codec2\components\avc\C2SoftAvcDec.cpp void C2SoftAvcDec::process( const std::unique_ptr<C2Work> &work, const std::shared_ptr<C2BlockPool> &pool) { ... uint32_t workIndex = work->input.ordinal.frameIndex.peeku() & 0xFFFFFFFF; C2ReadView rView = mDummyReadView; if (!work->input.buffers.empty()) { //关注buffers[0] rView = work->input.buffers[0]->data().linearBlocks().front().map().get(); inSize = rView.capacity(); } }
SimpleC2Component::processQueue()每次只处理一个work,处理完就把work回送上去。
\\av\media\codec2\components\base\SimpleC2Component.cpp bool SimpleC2Component::processQueue() { .... ALOGV("start processing frame #%" PRIu64, work->input.ordinal.frameIndex.peeku()); //处理work process(work, mOutputBlockPool); ALOGV("processed frame #%" PRIu64, work->input.ordinal.frameIndex.peeku()); Mutexed<WorkQueue>::Locked queue(mWorkQueue); if (work->workletsProcessed != 0u) { queue.unlock(); Mutexed<ExecState>::Locked state(mExecState); ALOGV("returning this work"); std::shared_ptr<C2Component::Listener> listener = state->mListener; state.unlock(); //回送work listener->onWorkDone_nb(shared_from_this(), vec(work)); } ... }
在没有新送下来的work需要处理的时候,processQueue()会调用drain接口作“渲染”操作,它会看解码器是否有帧数据生成,有的话,就填充到work中回送到上层。
\\av\media\codec2\components\base\SimpleC2Component.cpp bool SimpleC2Component::processQueue() { .... if (!work) { c2_status_t err = drain(drainMode, mOutputBlockPool); if (err != C2_OK) { Mutexed<ExecState>::Locked state(mExecState); std::shared_ptr<C2Component::Listener> listener = state->mListener; state.unlock(); listener->onError_nb(shared_from_this(), err); } return hasQueuedWork; } ... }
另一个渲染的地方是在process()中,解码完发现有帧数据的时候,就调用finishWork()将work回送。
\\av\media\codec2\components\avc\C2SoftAvcDec.cpp void C2SoftAvcDec::process( const std::unique_ptr<C2Work> &work, const std::shared_ptr<C2BlockPool> &pool) { ... if (s_decode_op.u4_output_present) { finishWork(s_decode_op.u4_ts, work); } ... }
5 小结
Component内部的逻辑还是比较好理解的,重点在于它是如何申请buffer的,如何将buffer“送”给解码器,解码完后是如何取得buffer并返回上层,难点在于work对象层层封装,当你要访问实际内存地址时,如何访问,如果要取得内存的handle,又要如何访问,这一点通过将work对象一层一层的“绘制”出来,就好懂得多。接下来问题来了,在OMX中,上下层的交互配置是通过setParamerter/getParamerter等接口进行的,那么在Codec2中是如何进行的?Codec2中到底有没有像OMX一样的BufferCountActual设计?Codec2在调用nativewindow的setMaxDequeuedBufferCount时是如何确定maxDequeueBufferCount的?GraphicBuffer的生命周期是如何控制的?
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