一、 简介
多媒体播放框架主要的实现在PlayerServer服务中,这个服务提供了媒体播放框架所需要的实现环境,继续跟踪代码分析发现,PlayerServer主要通过gstreamer适配层,对gstreamer进行调用。gstreamer属于更加具体的实现,所以本篇文章主要是分析PlayerServer通过适配层调用到gstreamer的过程。
此前,我在《OpenHarmony 3.2 Beta多媒体系列-音视频播放框架》一文中,主要分析了多媒体播放的框架层代码,本地接口通过服务端的proxy代理类进行IPC调用,最终调用到PlayerServer服务端。本篇主要分析了多媒体gstreamer的调用,涉及到从PlayerServer到gstreamer的整体流程。
二、 目录
gstreamer ├── BUILD.gn ├── common │ ├── BUILD.gn │ ├── playbin_adapter │ │ ├── i_playbin_ctrler.h │ │ ├── playbin2_ctrler.cpp │ │ ├── playbin2_ctrler.h │ │ ├── playbin_ctrler_base.cpp │ │ ├── playbin_ctrler_base.h │ │ ├── playbin_msg_define.h │ │ ├── playbin_sink_provider.h │ │ ├── playbin_state.cpp │ │ ├── playbin_state.h │ │ ├── playbin_task_mgr.cpp │ │ └── playbin_task_mgr.h │ ├── state_machine │ │ ├── state_machine.cpp │ │ └── state_machine.h ├── factory │ ├── BUILD.gn │ └── engine_factory.cpp └── player ├── BUILD.gn ├── player_codec_ctrl.cpp ├── player_codec_ctrl.h ├── player_engine_gst_impl.cpp ├── player_engine_gst_impl.h ├── player_sinkprovider.cpp ├── player_sinkprovider.h ├── player_track_parse.cpp └── player_track_parse.h
目录主要是多媒体子系统中的engine部分,涉及到了gstreamer的适配层,gstreamer具体的实现是在third_party/gstreamer目录中。
三 、Gstreamer介绍
1. 简介
Gstreamer是一个跨平台的多媒体框架,应用程序可以通过管道(Pipeline)的方式,将多媒体处理的各个步骤串联起来,达到预期的效果。每个步骤通过元素(Element)基于GObject对象系统通过插件(plugins)的方式实现,方便了各项功能的扩展。
2.Gstreamer几个重要的概念
Element
Element是Gstreamer中最重要的对象类型之一。一个element实现一个功能(读取文件,解码,输出等),程序需要创建多个element,并按顺序将其串联起来,构成一个完整的Pipeline。
Pad
Pad是一个element的输入/输出接口,分为src pad(生产数据)和sink pad(消费数据)两种。
两个element必须通过pad才能连接起来,pad拥有当前element能处理数据类型的能力(capabilities),会在连接时通过比较src pad和sink pad中所支持的能力,来选择最恰当的数据类型用于传输,如果element不支持,程序会直接退出。在element通过pad连接成功后,数据会从上一个element的src pad传到下一个element的sink pad然后进行处理。
Bin和Pipeline
Bin是一个容器,用于管理多个element,改变bin的状态时,bin会自动去修改所包含的element的状态,也会转发所收到的消息。如果没有bin,我们需要依次操作我们所使用的element。通过bin降低了应用的复杂度。
Pipeline继承自bin,为程序提供一个bus用于传输消息,并且对所有子element进行同步。当将Pipeline的状态设置为PLAYING时,Pipeline会在一个/多个新的线程中通过element处理数据。
四、调用流程![](/i/l/?n=22&i=blog/2824423/202211/2824423-20221124103130521-1597068882.png)
五、源码分析
1. PrepareAsync分析
首先,在PlayerServer的PrepareAsync中会调用OnPrepare(false),具体是在OnPrepare(false)中实现,参数传入false,表明调用的是异步方法。
int32_t PlayerServer::PrepareAsync() { std::lock_guard<std::mutex> lock(mutex_); MEDIA_LOGW("KPI-TRACE: PlayerServer PrepareAsync in"); if (lastOpStatus_ == PLAYER_INITIALIZED || lastOpStatus_ == PLAYER_STOPPED) { return OnPrepare(false); } else { MEDIA_LOGE("Can not Prepare, currentState is %{public}s", GetStatusDescription(lastOpStatus_).c_str()); return MSERR_INVALID_OPERATION; } }
OnPrepare方法中,先通过playerEngine_调用SerVideoSurface的方法,将surface_设置到PlayerEngineGstImpl中(producerSurface_),接着启动一个任务,调用目前状态的Prepare()方法。
int32_t PlayerServer::OnPrepare(bool sync) { CHECK_AND_RETURN_RET_LOG(playerEngine_ != nullptr, MSERR_NO_MEMORY, "playerEngine_ is nullptr"); int32_t ret = MSERR_OK; #ifdef SUPPORT_VIDEO if (surface_ != nullptr) { ret = playerEngine_->SetVideoSurface(surface_); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, MSERR_INVALID_OPERATION, "Engine SetVideoSurface Failed!"); } #endif lastOpStatus_ = PLAYER_PREPARED; auto preparedTask = std::make_shared<TaskHandler<int32_t>>([this]() { MediaTrace::TraceBegin("PlayerServer::PrepareAsync", FAKE_POINTER(this)); auto currState = std::static_pointer_cast<BaseState>(GetCurrState()); return currState->Prepare(); }); ret = taskMgr_.LaunchTask(preparedTask, PlayerServerTaskType::STATE_CHANGE); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, ret, "Prepare launch task failed"); if (sync) { (void)preparedTask->GetResult(); // wait HandlePrpare } return MSERR_OK; }
进入Preparing状态后,会触发PlayerServer的HandlePrepare()方法被调用,在这个方法里会通过playerEngine_调用PrepareAsync方法,这个方法调用的是PlayerEngineGstImpl对应的PrepareAsync方法。
int32_t PlayerServer::HandlePrepare() { int32_t ret = playerEngine_->PrepareAsync(); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, MSERR_INVALID_OPERATION, "Server Prepare Failed!"); if (config_.leftVolume <= 1.0f || config_.rightVolume <= 1.0f) { ret = playerEngine_->SetVolume(config_.leftVolume, config_.rightVolume); MEDIA_LOGD("Prepared SetVolume leftVolume:%{public}f rightVolume:%{public}f, ret:%{public}d", \ config_.leftVolume, config_.rightVolume, ret); } (void)playerEngine_->SetLooping(config_.looping); { auto rateTask = std::make_shared<TaskHandler<void>>([this]() { auto currState = std::static_pointer_cast<BaseState>(GetCurrState()); (void)currState->SetPlaybackSpeed(config_.speedMode); }); (void)taskMgr_.LaunchTask(rateTask, PlayerServerTaskType::RATE_CHANGE); } return MSERR_OK; }
首先初始化playBinCtrler_,后续的操作都是通过PlayBinCtrlerBase对象来操作的,所以PlayBinCtrlerInit()方法会创建PlayBinCtrlerBase对象(playBinCtrler_),创建好以后通过playBinCtrler_进行SetSource和SetXXXListener的设置。
int32_t PlayerEngineGstImpl::PrepareAsync() { std::unique_lock<std::mutex> lock(mutex_); MEDIA_LOGD("Prepare in"); int32_t ret = PlayBinCtrlerInit(); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, MSERR_INVALID_VAL, "PlayBinCtrlerInit failed"); CHECK_AND_RETURN_RET_LOG(playBinCtrler_ != nullptr, MSERR_INVALID_VAL, "playBinCtrler_ is nullptr"); ret = playBinCtrler_->PrepareAsync(); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, ret, "PrepareAsync failed"); // The duration of some resources without header information cannot be obtained. MEDIA_LOGD("Prepared ok out"); return MSERR_OK; }
初始化完成以后,接下来进行playBinCtrler_的PrepareAsync的调用,PlayBinCtrlerBase中的PrepareAsync的方法间接地调用了PrepareAsyncInternal。
int32_t PlayBinCtrlerBase::PrepareAsync() { MEDIA_LOGD("enter"); std::unique_lock<std::mutex> lock(mutex_); return PrepareAsyncInternal(); }
PrepareAsyncInternal首先判断当前的状态,如果是preparingState或preparedState,那么就直接返回成功,否则继续向下调用。接下来会调用EnterInitializedState(),这个方法中会创建playbin,设置signal的回调以及gstreamer参数的设置。最后调用目前状态的Prepare方法,此时的状态是InitializedState。
int32_t PlayBinCtrlerBase::PrepareAsyncInternal() { if ((GetCurrState() == preparingState_) || (GetCurrState() == preparedState_)) { MEDIA_LOGI("already at preparing state, skip"); return MSERR_OK; } CHECK_AND_RETURN_RET_LOG((!uri_.empty() || appsrcWrap_), MSERR_INVALID_OPERATION, "Set uri firsty!"); int32_t ret = EnterInitializedState(); CHECK_AND_RETURN_RET(ret == MSERR_OK, ret); auto currState = std::static_pointer_cast<BaseState>(GetCurrState()); ret = currState->Prepare(); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, ret, "PrepareAsyncInternal failed"); return MSERR_OK; }
InitializedState的Prepare方法又通过ctrler_调回到PlayBinCtrlerBase的ChangeState方法,这个方法是在PlayBinCtrlerBase的父类StateMachine中,它是一个状态机,管理着各种状态的切换。
int32_t PlayBinCtrlerBase::InitializedState::Prepare() { ctrler_.ChangeState(ctrler_.preparingState_); return MSERR_OK; }
很多表示状态的类在PlayBinCtrlerBase中进行声明,这些子类的具体实现功能在playbin_state.cpp中。
private: class BaseState; class IdleState; class InitializedState; class PreparingState; class PreparedState; class PlayingState; class PausedState; class StoppedState; class StoppingState; class PlaybackCompletedState;
接下来看一下状态机的ChangeState方法,可以看出切换状态的时候,先调用切换前状态的StateExit()方法,再调用切换后状态的StateEnter()。如果需要一些操作,我们可以在状态的StateEnter和StateExit中进行。
void StateMachine::ChangeState(const std::shared_ptr<State> &state) { ...... if (currState_ != nullptr && currState_->GetStateName() == "stopping_state" && state->GetStateName() != "stopped_state") { return; } if (currState_) { currState_->StateExit(); } currState_ = state; state->StateEnter(); }
因为上面切换状态调用的是ctrler_.ChangeState(ctrler_.preparingState_),所以接下来看一下PreparingState状态的StateEnter方法。这个方法中首先是调用了ctrler_.ReportMessage(msg),字面上看是用来上报msg信息的。
void PlayBinCtrlerBase::PreparingState::StateEnter() { PlayBinMessage msg = { PLAYBIN_MSG_SUBTYPE, PLAYBIN_SUB_MSG_BUFFERING_START, 0, {} }; ctrler_.ReportMessage(msg); GstStateChangeReturn ret; (void)ChangePlayBinState(GST_STATE_PAUSED, ret); MEDIA_LOGD("PreparingState::StateEnter finished"); }
ctrler_是PlayBinCtrlerBase类型的变量,直接看PlayBinCtrlerBase的ReportMessage方法,这个方法的核心,是创建一个任务后,将任务放入消息队列中,等待消息被处理,这里我们最想知道的是这个消息会在什么地方被处理。msgReportHandler创建了TaskHandler,这个里面会调用notifier_(msg),这里的notifier_比较重要,我们可以顺着这个变量向上分析。
void PlayBinCtrlerBase::ReportMessage(const PlayBinMessage &msg) { ...... auto msgReportHandler = std::make_shared<TaskHandler<void>>([this, msg]() { notifier_(msg); }); int32_t ret = msgQueue_->EnqueueTask(msgReportHandler); if (ret != MSERR_OK) { MEDIA_LOGE("async report msg failed, type: %{public}d, subType: %{public}d, code: %{public}d", msg.type, msg.subType, msg.code); }; if (msg.type == PlayBinMsgType::PLAYBIN_MSG_EOS) { ProcessEndOfStream(); } }
notifier_是在PlayBinCtrlerBase被创建的时候赋值的。
PlayBinCtrlerBase::PlayBinCtrlerBase(const PlayBinCreateParam &createParam) : renderMode_(createParam.renderMode), notifier_(createParam.notifier), sinkProvider_(createParam.sinkProvider) { MEDIA_LOGD("enter ctor, instance: 0x%{public}06" PRIXPTR "", FAKE_POINTER(this)); }
在源码分析的前期PlayerEngineGstImpl初始化PlayBinCtrlerBase的时候进行了创建notifier = std::bind(&PlayerEngineGstImpl::OnNotifyMessage, this, std::placeholders::_1) notifier相当于是调用了PlayerEngineGstImpl::OnNotifyMessage方法。所以上述中的处理函数就是PlayerEngineGstImpl::OnNotifyMessage。
int32_t PlayerEngineGstImpl::PlayBinCtrlerPrepare() { uint8_t renderMode = IPlayBinCtrler::PlayBinRenderMode::DEFAULT_RENDER; auto notifier = std::bind(&PlayerEngineGstImpl::OnNotifyMessage, this, std::placeholders::_1); { std::unique_lock<std::mutex> lk(trackParseMutex_); sinkProvider_ = std::make_shared<PlayerSinkProvider>(producerSurface_); sinkProvider_->SetAppInfo(appuid_, apppid_); } IPlayBinCtrler::PlayBinCreateParam createParam = { static_cast<IPlayBinCtrler::PlayBinRenderMode>(renderMode), notifier, sinkProvider_ }; playBinCtrler_ = IPlayBinCtrler::Create(IPlayBinCtrler::PlayBinKind::PLAYBIN2, createParam); ...... return MSERR_OK; }
在OnNotifyMessage中指定了各种消息类型对应的执行函数,上述代码中创建的Message类型是PLAYBIN_MSG_SUBTYPE,子类型为PLAYBIN_SUB_MSG_BUFFERING_START。
void PlayerEngineGstImpl::OnNotifyMessage(const PlayBinMessage &msg) { const std::unordered_map<int32_t, MsgNotifyFunc> MSG_NOTIFY_FUNC_TABLE = { { PLAYBIN_MSG_ERROR, std::bind(&PlayerEngineGstImpl::HandleErrorMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_SEEKDONE, std::bind(&PlayerEngineGstImpl::HandleSeekDoneMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_SPEEDDONE, std::bind(&PlayerEngineGstImpl::HandleInfoMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_BITRATEDONE, std::bind(&PlayerEngineGstImpl::HandleInfoMessage, this, std::placeholders::_1)}, { PLAYBIN_MSG_EOS, std::bind(&PlayerEngineGstImpl::HandleInfoMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_STATE_CHANGE, std::bind(&PlayerEngineGstImpl::HandleInfoMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_SUBTYPE, std::bind(&PlayerEngineGstImpl::HandleSubTypeMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_AUDIO_SINK, std::bind(&PlayerEngineGstImpl::HandleAudioMessage, this, std::placeholders::_1) }, { PLAYBIN_MSG_POSITION_UPDATE, std::bind(&PlayerEngineGstImpl::HandlePositionUpdateMessage, this, std::placeholders::_1) }, }; if (MSG_NOTIFY_FUNC_TABLE.count(msg.type) != 0) { MSG_NOTIFY_FUNC_TABLE.at(msg.type)(msg); } }
最终的流程走到了PlayerEngineGstImpl::HandleBufferingStart(),在这个方法中,主要通过obs_将format传给IPlayerEngineObs的OnInfo方法。
void PlayerEngineGstImpl::HandleBufferingStart() { percent_ = 0; Format format; (void)format.PutIntValue(std::string(PlayerKeys::PLAYER_BUFFERING_START), 0); std::shared_ptr<IPlayerEngineObs> notifyObs = obs_.lock(); if (notifyObs != nullptr) { notifyObs->OnInfo(INFO_TYPE_BUFFERING_UPDATE, 0, format); } }
我们重点看一下obs_是哪里设置的,在PlayerServer的初始化InitPlayEngine。shared_from_this()相当于是把PlayerServer自身赋值给obs,PlayerServer也是实现了IPlayerEngineObs对应的接口。
int32_t PlayerServer::InitPlayEngine(const std::string &url) { ...... int32_t ret = taskMgr_.Init(); auto engineFactory = EngineFactoryRepo::Instance().GetEngineFactory(IEngineFactory::Scene::SCENE_PLAYBACK, url); playerEngine_ = engineFactory->CreatePlayerEngine(appUid_, appPid_); if (dataSrc_ == nullptr) { ret = playerEngine_->SetSource(url); } else { ret = playerEngine_->SetSource(dataSrc_); } std::shared_ptr<IPlayerEngineObs> obs = shared_from_this(); ret = playerEngine_->SetObs(obs); lastOpStatus_ = PLAYER_INITIALIZED; ChangeState(initializedState_); return MSERR_OK; }
这样我们就跟踪到了PlayerServer的OnInfo()方法。
void PlayerServer::OnInfo(PlayerOnInfoType type, int32_t extra, const Format &infoBody) { std::lock_guard<std::mutex> lockCb(mutexCb_); int32_t ret = HandleMessage(type, extra, infoBody); if (playerCb_ != nullptr && ret == MSERR_OK) { playerCb_->OnInfo(type, extra, infoBody); } }
2. Play分析
从PlayerServer开始跟踪,调用到PlayerServer的OnPlay()方法。
int32_t PlayerServer::Play() { ...... if (lastOpStatus_ == PLAYER_PREPARED || lastOpStatus_ == PLAYER_PLAYBACK_COMPLETE || lastOpStatus_ == PLAYER_PAUSED) { return OnPlay(); } else { return MSERR_INVALID_OPERATION; } }
在OnPlay中会启动一个任务,在任务中获取当前的状态,然后调用当前状态的Play()方法。
int32_t PlayerServer::OnPlay() { ...... auto playingTask = std::make_shared<TaskHandler<void>>([this]() { auto currState = std::static_pointer_cast<BaseState>(GetCurrState()); (void)currState->Play(); }); int ret = taskMgr_.LaunchTask(playingTask, PlayerServerTaskType::STATE_CHANGE); lastOpStatus_ = PLAYER_STARTED; return MSERR_OK; }
前面调用了PrepareAsync,所以当前的状态是Prepared,调用到了PreparedState的Play()方法,这个方法还是按照之前Prepare的方式,调回到PlayerServer的HandlePlay()。
int32_t PlayerServer::PreparedState::Play() { return server_.HandlePlay(); }
在PlayServer中通过播放引擎继续向下调用。
int32_t PlayerServer::HandlePlay() { int32_t ret = playerEngine_->Play(); CHECK_AND_RETURN_RET_LOG(ret == MSERR_OK, MSERR_INVALID_OPERATION, "Engine Play Failed!"); return MSERR_OK; }
在PlayerEngineGstImpl的Play()方法会继续调用playBinCtrler_的Play()方法。
int32_t PlayerEngineGstImpl::Play() { ...... playBinCtrler_->Play(); return MSERR_OK; }
PlayBinCtrlerBase的Play()方法根据当前的State,调用currSate->Play()。
int32_t PlayBinCtrlerBase::Play() { ...... auto currState = std::static_pointer_cast<BaseState>(GetCurrState()); int32_t ret = currState->Play(); return MSERR_OK; }
在PreparedState的Play()方法中改变了PlayBin的状态为playing。
int32_t PlayBinCtrlerBase::PreparedState::Play() { GstStateChangeReturn ret; return ChangePlayBinState(GST_STATE_PLAYING, ret); }
ChangePlayBinState主要是调用了
gst_element_set_state(GST_ELEMENT_CAST(ctrler_.playbin_),GST_STATE_PLAYING),这个直接调用了gstreamer三方库的实现,调用完这个方法以后,gstreamer就开始进行播放了。
int32_t PlayBinCtrlerBase::BaseState::ChangePlayBinState(GstState targetState, GstStateChangeReturn &ret) { ...... ret = gst_element_set_state(GST_ELEMENT_CAST(ctrler_.playbin_), targetState); if (ret == GST_STATE_CHANGE_FAILURE) { MEDIA_LOGE("Failed to change playbin's state to %{public}s", gst_element_state_get_name(targetState)); return MSERR_INVALID_OPERATION; } return MSERR_OK; }
六、总结
本篇文章主要从PlayerServer播放服务开始分析音视频播放的流程,涉及到gstreamer引擎的调用,相对于多媒体播放框架来说,更加底层,便于熟悉从框架到gstreamer的整体流程。
标签:std,OpenHarmony,调用,int32,gstreamer,ret,音视频,PlayerServer,MSERR From: https://www.cnblogs.com/openharmony/p/16921089.html