OpenHarmony 3.2 Beta多媒体系列—

一、简介

媒体子系统为开发者提供了媒体相关的很多功能，本文针对其中的视频录制功能做个详细的介绍。首先，我将通过媒体子系统提供的视频录制Test代码作为切入点，给大家梳理一下整个录制的流程。

二、目录

foundation/multimedia/camera_framework

├── frameworks

│   ├── js

│   │   └── camera_napi                            #napi实现

│   │       └── src

│   │           ├── input                          #Camera输入

│   │           ├── output                         #Camera输出

│   │           └── session                        #会话管理

│   └── native                                     #native实现

│       └── camera

│           ├── BUILD.gn

│           ├── src

│           │   ├── input                          #Camera输入

│           │   ├── output                         #Camera输出

│           │   └── session                        #会话管理

├── interfaces                                     #接口定义

│   ├── inner_api                                  #内部native实现

│   │   └── native

│   │       ├── camera

│   │       │   └── include

│   │       │       ├── input

│   │       │       ├── output

│   │       │       └── session

│   └── kits                                       #napi接口

│       └── js

│           └── camera_napi

│               ├── BUILD.gn

│               ├── include

│               │   ├── input

│               │   ├── output

│               │   └── session

│               └── @ohos.multimedia.camera.d.ts

└── services                                       #服务端

    └── camera_service

        ├── binder

        │   ├── base

        │   ├── client                             #IPC的客户端

        │   │   └── src

        │   └── server                             #IPC的服务端

        │       └── src

        └── src

三、录制的总体流程

四、Native接口使用

在OpenAtom OpenHarmony（以下简称“OpenHarmony”）系统中，多媒体子系统通过N-API接口提供给上层JS调用，N-API相当于是JS和Native之间的桥梁，在OpenHarmony源码中，提供了C++直接调用视频录制功能的例子，foundation/multimedia/camera_framework/interfaces/inner_api/native/test目录中。本文章主要参考了camera_video.cpp文件中的视频录制流程。

首先根据camera_video.cpp的main方法，了解下视频录制的主要流程代码。

int main(int argc, char **argv)

{

    ......

    // 创建CameraManager实例

    sptr<CameraManager> camManagerObj = CameraManager::GetInstance();

    // 设置回调

    camManagerObj->SetCallback(std::make_shared<TestCameraMngerCallback>(testName));

    // 获取支持的相机设备列表

    std::vector<sptr<CameraDevice>> cameraObjList = camManagerObj->GetSupportedCameras();

    // 创建采集会话

    sptr<CaptureSession> captureSession = camManagerObj->CreateCaptureSession();

    // 开始配置采集会话

    captureSession->BeginConfig();

    // 创建CameraInput

    sptr<CaptureInput> captureInput = camManagerObj->CreateCameraInput(cameraObjList[0]);

    sptr<CameraInput> cameraInput = (sptr<CameraInput> &)captureInput;

    // 开启CameraInput

    cameraInput->Open();

    // 设置CameraInput的Error回调

    cameraInput->SetErrorCallback(std::make_shared<TestDeviceCallback>(testName));

    // 添加CameraInput实例到采集会话中

    ret = captureSession->AddInput(cameraInput);

    sptr<Surface> videoSurface = nullptr;

    std::shared_ptr<Recorder> recorder = nullptr;

    // 创建Video的Surface

    videoSurface = Surface::CreateSurfaceAsConsumer();

    sptr<SurfaceListener> videoListener = new SurfaceListener("Video", SurfaceType::VIDEO, g_videoFd, videoSurface);

    // 注册Surface的事件监听

    videoSurface->RegisterConsumerListener((sptr<IBufferConsumerListener> &)videoListener);

    // 视频的配置

    VideoProfile videoprofile = VideoProfile(static_cast<CameraFormat>(videoFormat), videosize, videoframerates);

    // 创建VideoOutput实例

    sptr<CaptureOutput> videoOutput = camManagerObj->CreateVideoOutput(videoprofile, videoSurface);

    // 设置VideoOutput的回调

    ((sptr<VideoOutput> &)videoOutput)->SetCallback(std::make_shared<TestVideoOutputCallback>(testName));

    // 添加videoOutput到采集会话中

    ret = captureSession->AddOutput(videoOutput);

    // 提交会话配置

    ret = captureSession->CommitConfig();

    // 开始录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Start();

    sleep(videoPauseDuration);

    MEDIA_DEBUG_LOG("Resume video recording");

    // 暂停录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Resume();

    MEDIA_DEBUG_LOG("Wait for 5 seconds before stop");

    sleep(videoCaptureDuration);

    MEDIA_DEBUG_LOG("Stop video recording");

    // 停止录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Stop();

    MEDIA_DEBUG_LOG("Closing the session");

    // 停止采集会话

    ret = captureSession->Stop();

    MEDIA_DEBUG_LOG("Releasing the session");

    // 释放会话采集

    captureSession->Release();

//Close video file

TestUtils::SaveVideoFile(nullptr,0,VideoSaveMode::CLOSE, g_videoFd);

    cameraInput->Release();

    camManagerObj->SetCallback(nullptr);

    return 0;

}

以上是视频录制的整体流程，其过程主要通过Camera模块支持的能力来实现，其中涉及几个重要的类：CaptureSession、CameraInput、VideoOutput。CaptureSession是整个过程的控制者，CameraInput和VideoOutput相当于是设备的输入和输出。

五、调用流程

int main(int argc, char **argv)

{

    ......

    // 创建CameraManager实例

    sptr<CameraManager> camManagerObj = CameraManager::GetInstance();

    // 设置回调

    camManagerObj->SetCallback(std::make_shared<TestCameraMngerCallback>(testName));

    // 获取支持的相机设备列表

    std::vector<sptr<CameraDevice>> cameraObjList = camManagerObj->GetSupportedCameras();

    // 创建采集会话

    sptr<CaptureSession> captureSession = camManagerObj->CreateCaptureSession();

    // 开始配置采集会话

    captureSession->BeginConfig();

    // 创建CameraInput

    sptr<CaptureInput> captureInput = camManagerObj->CreateCameraInput(cameraObjList[0]);

    sptr<CameraInput> cameraInput = (sptr<CameraInput> &)captureInput;

    // 开启CameraInput

    cameraInput->Open();

    // 设置CameraInput的Error回调

    cameraInput->SetErrorCallback(std::make_shared<TestDeviceCallback>(testName));

    // 添加CameraInput实例到采集会话中

    ret = captureSession->AddInput(cameraInput);

    sptr<Surface> videoSurface = nullptr;

    std::shared_ptr<Recorder> recorder = nullptr;

    // 创建Video的Surface

    videoSurface = Surface::CreateSurfaceAsConsumer();

    sptr<SurfaceListener> videoListener = new SurfaceListener("Video", SurfaceType::VIDEO, g_videoFd, videoSurface);

    // 注册Surface的事件监听

    videoSurface->RegisterConsumerListener((sptr<IBufferConsumerListener> &)videoListener);

    // 视频的配置

    VideoProfile videoprofile = VideoProfile(static_cast<CameraFormat>(videoFormat), videosize, videoframerates);

    // 创建VideoOutput实例

    sptr<CaptureOutput> videoOutput = camManagerObj->CreateVideoOutput(videoprofile, videoSurface);

    // 设置VideoOutput的回调

    ((sptr<VideoOutput> &)videoOutput)->SetCallback(std::make_shared<TestVideoOutputCallback>(testName));

    // 添加videoOutput到采集会话中

    ret = captureSession->AddOutput(videoOutput);

    // 提交会话配置

    ret = captureSession->CommitConfig();

    // 开始录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Start();

    sleep(videoPauseDuration);

    MEDIA_DEBUG_LOG("Resume video recording");

    // 暂停录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Resume();

    MEDIA_DEBUG_LOG("Wait for 5 seconds before stop");

    sleep(videoCaptureDuration);

    MEDIA_DEBUG_LOG("Stop video recording");

    // 停止录制

    ret = ((sptr<VideoOutput> &)videoOutput)->Stop();

    MEDIA_DEBUG_LOG("Closing the session");

    // 停止采集会话

    ret = captureSession->Stop();

    MEDIA_DEBUG_LOG("Releasing the session");

    // 释放会话采集

    captureSession->Release();

//Close video file

TestUtils::SaveVideoFile(nullptr,0,VideoSaveMode::CLOSE, g_videoFd);

    cameraInput->Release();

    camManagerObj->SetCallback(nullptr);

    return 0;

}

后续主要针对上面的调用流程，梳理具体的调用流程，方便我们对了解视频录制的整理架构有一个更加深入的了解。

1. 创建CameraManager实例

通过CameraManager::GetInstance()获取CameraManager的实例，后续的一些接口都是通过该实例进行调用的。GetInstance使用了单例模式，在OpenHarmony代码中这种方式很常见。

sptr<CameraManager> &CameraManager::GetInstance()

{

    if (CameraManager::cameraManager_ == nullptr) {

        MEDIA_INFO_LOG("Initializing camera manager for first time!");

        CameraManager::cameraManager_ = new(std::nothrow) CameraManager();

        if (CameraManager::cameraManager_ == nullptr) {

            MEDIA_ERR_LOG("CameraManager::GetInstance failed to new CameraManager");

        }

    }

    return CameraManager::cameraManager_;

}

2. 获取支持的相机设备列表

通过调用CameraManager的GetSupportedCameras()接口，获取设备支持的CameraDevice列表。跟踪代码可以发现serviceProxy_->GetCameras最终会调用到Camera服务端的对应接口。

std::vector<sptr<CameraDevice>> CameraManager::GetSupportedCameras()

{

    CAMERA_SYNC_TRACE;

    std::lock_guard<std::mutex> lock(mutex_);

    std::vector<std::string> cameraIds;

    std::vector<std::shared_ptr<Camera::CameraMetadata>> cameraAbilityList;

    int32_t retCode = -1;

    sptr<CameraDevice> cameraObj = nullptr;

    int32_t index = 0;

    if (cameraObjList.size() > 0) {

        cameraObjList.clear();

    }

    if (serviceProxy_ == nullptr) {

        MEDIA_ERR_LOG("CameraManager::GetCameras serviceProxy_ is null, returning empty list!");

        return cameraObjList;

    }

    std::vector<sptr<CameraDevice>> supportedCameras;

    retCode = serviceProxy_->GetCameras(cameraIds, cameraAbilityList);

    if (retCode == CAMERA_OK) {

        for (auto& it : cameraIds) {

            cameraObj = new(std::nothrow) CameraDevice(it, cameraAbilityList[index++]);

            if (cameraObj == nullptr) {

                MEDIA_ERR_LOG("CameraManager::GetCameras new CameraDevice failed for id={public}%s", it.c_str());

                continue;

            }

            supportedCameras.emplace_back(cameraObj);

        }

    } else {

        MEDIA_ERR_LOG("CameraManager::GetCameras failed!, retCode: %{public}d", retCode);

    }

    ChooseDeFaultCameras(supportedCameras);

    return cameraObjList;

}

3. 创建采集会话

下面是比较重要的环节，通过调用CameraManager的CreateCaptureSession接口创建采集会话。CameraManager创建采集会话，是通过serviceProxy_->CreateCaptureSession方式进行调用，这里涉及到了OpenHarmony中的IPC的调用，serviceProxy_是远端服务在本地的代理，通过这个代理可以调用到具体的服务端，这里是HCameraService。

sptr<CaptureSession> CameraManager::CreateCaptureSession()

{

    CAMERA_SYNC_TRACE;

    sptr<ICaptureSession> captureSession = nullptr;

    sptr<CaptureSession> result = nullptr;

    int32_t retCode = CAMERA_OK;

    if (serviceProxy_ == nullptr) {

        MEDIA_ERR_LOG("CameraManager::CreateCaptureSession serviceProxy_ is null");

        return nullptr;

    }

    retCode = serviceProxy_->CreateCaptureSession(captureSession);

    if (retCode == CAMERA_OK && captureSession != nullptr) {

        result = new(std::nothrow) CaptureSession(captureSession);

        if (result == nullptr) {

            MEDIA_ERR_LOG("Failed to new CaptureSession");

        }

    } else {

        MEDIA_ERR_LOG("Failed to get capture session object from hcamera service!, %{public}d", retCode);

    }

    return result;

}

代码最终来到HCameraService::CreateCaptureSession中，该方法中new了一个HCaptureSession对象，并且将该对象传递给了参数session，所以前面的captureSession对象就是这里new出来的HCaptureSession，前面的CameraManager的CreateCaptureSession()方法中将captureSession封装成CaptureSession对象返回给应用层使用。

int32_t HCameraService::CreateCaptureSession(sptr<ICaptureSession> &session)

{

    CAMERA_SYNC_TRACE;

    sptr<HCaptureSession> captureSession;

    if (streamOperatorCallback_ == nullptr) {

        streamOperatorCallback_ = new(std::nothrow) StreamOperatorCallback();

        if (streamOperatorCallback_ == nullptr) {

            MEDIA_ERR_LOG("HCameraService::CreateCaptureSession streamOperatorCallback_ allocation failed");

            return CAMERA_ALLOC_ERROR;

        }

    }

    std::lock_guard<std::mutex> lock(mutex_);

    OHOS::Security::AccessToken::AccessTokenID callerToken = IPCSkeleton::GetCallingTokenID();

    captureSession = new(std::nothrow) HCaptureSession(cameraHostManager_, streamOperatorCallback_, callerToken);

    if (captureSession == nullptr) {

        MEDIA_ERR_LOG("HCameraService::CreateCaptureSession HCaptureSession allocation failed");

        return CAMERA_ALLOC_ERROR;

    }

    session = captureSession;

    return CAMERA_OK;

}

4. 开始配置采集会话

调用CaptureSession的BeginConfig进行采集会话的配置工作。这个工作最终调用到被封装的HCaptureSession中。

int32_t HCaptureSession::BeginConfig()

{

    CAMERA_SYNC_TRACE;

    if (curState_ == CaptureSessionState::SESSION_CONFIG_INPROGRESS) {

        MEDIA_ERR_LOG("HCaptureSession::BeginConfig Already in config inprogress state!");

        return CAMERA_INVALID_STATE;

    }

    std::lock_guard<std::mutex> lock(sessionLock_);

    prevState_ = curState_;

    curState_ = CaptureSessionState::SESSION_CONFIG_INPROGRESS;

    tempCameraDevices_.clear();

    tempStreams_.clear();

    deletedStreamIds_.clear();

    return CAMERA_OK;

}

5. 创建CameraInput

应用层通过camManagerObj->CreateCameraInput(cameraObjList[0])的方式进行CameraInput的创建，cameraObjList[0]就是前面获取支持设备的第一个。根据CameraDevice创建对应的CameraInput对象。

sptr<CameraInput> CameraManager::CreateCameraInput(sptr<CameraDevice> &camera)

{

    CAMERA_SYNC_TRACE;

    sptr<CameraInput> cameraInput = nullptr;

    sptr<ICameraDeviceService> deviceObj = nullptr;

    if (camera != nullptr) {

        deviceObj = CreateCameraDevice(camera->GetID());

        if (deviceObj != nullptr) {

            cameraInput = new(std::nothrow) CameraInput(deviceObj, camera);

            if (cameraInput == nullptr) {

                MEDIA_ERR_LOG("failed to new CameraInput Returning null in CreateCameraInput");

                return cameraInput;

            }

        } else {

            MEDIA_ERR_LOG("Returning null in CreateCameraInput");

        }

    } else {

        MEDIA_ERR_LOG("CameraManager::CreateCameraInput: Camera object is null");

    }

    return cameraInput;

}

6. 开启CameraInput

调用了CameraInput的Open方法，进行输入设备的启动打开。

void CameraInput::Open()

{

    int32_t retCode = deviceObj_->Open();

    if (retCode != CAMERA_OK) {

        MEDIA_ERR_LOG("Failed to open Camera Input, retCode: %{public}d", retCode);

    }

}

7. 添加CameraInput实例到采集会话中

通过调用captureSession的AddInput方法，将创建的CameraInput对象添加到采集会话的输入中，这样采集会话就知道采集输入的设备。


int32_t CaptureSession::AddInput(sptr<CaptureInput> &input)

{

    CAMERA_SYNC_TRACE;

    if (input == nullptr) {

        MEDIA_ERR_LOG("CaptureSession::AddInput input is null");

        return CAMERA_INVALID_ARG;

    }

    input->SetSession(this);

    inputDevice_ = input;

    return captureSession_->AddInput(((sptr<CameraInput> &)input)->GetCameraDevice());

}

最终调用到HCaptureSession的AddInput方法，该方法中核心的代码是tempCameraDevices_.emplace_back(localCameraDevice)，将需要添加的CameraDevice插入到tempCameraDevices_容器中。

int32_t HCaptureSession::AddInput(sptr<ICameraDeviceService> cameraDevice)

{

    CAMERA_SYNC_TRACE;

    sptr<HCameraDevice> localCameraDevice = nullptr;

    if (cameraDevice == nullptr) {

        MEDIA_ERR_LOG("HCaptureSession::AddInput cameraDevice is null");

        return CAMERA_INVALID_ARG;

    }

    if (curState_ != CaptureSessionState::SESSION_CONFIG_INPROGRESS) {

        MEDIA_ERR_LOG("HCaptureSession::AddInput Need to call BeginConfig before adding input");

        return CAMERA_INVALID_STATE;

    }

    if (!tempCameraDevices_.empty() || (cameraDevice_ != nullptr && !cameraDevice_->IsReleaseCameraDevice())) {

        MEDIA_ERR_LOG("HCaptureSession::AddInput Only one input is supported");

        return CAMERA_INVALID_SESSION_CFG;

    }

    localCameraDevice = static_cast<HCameraDevice*>(cameraDevice.GetRefPtr());

    if (cameraDevice_ == localCameraDevice) {

        cameraDevice_->SetReleaseCameraDevice(false);

    } else {

        tempCameraDevices_.emplace_back(localCameraDevice);

        CAMERA_SYSEVENT_STATISTIC(CreateMsg("CaptureSession::AddInput"));

    }

    sptr<IStreamOperator> streamOperator;

    int32_t rc = localCameraDevice->GetStreamOperator(streamOperatorCallback_, streamOperator);

    if (rc != CAMERA_OK) {

        MEDIA_ERR_LOG("HCaptureSession::GetCameraDevice GetStreamOperator returned %{public}d", rc);

        localCameraDevice->Close();

        return rc;

    }

    return CAMERA_OK;

}

8. 创建Video的Surface

通过Surface::CreateSurfaceAsConsumer创建Surface。

sptr<Surface> Surface::CreateSurfaceAsConsumer(std::string name, bool isShared)

{

    sptr<ConsumerSurface> surf = new ConsumerSurface(name, isShared);

    GSError ret = surf->Init();

    if (ret != GSERROR_OK) {

        BLOGE("Failure, Reason: consumer surf init failed");

        return nullptr;

    }

    return surf;

}

9. 创建VideoOutput实例

通过调用CameraManager的CreateVideoOutput来创建VideoOutput实例。

sptr<VideoOutput> CameraManager::CreateVideoOutput(VideoProfile &profile, sptr<Surface> &surface)

{

    CAMERA_SYNC_TRACE;

    sptr<IStreamRepeat> streamRepeat = nullptr;

    sptr<VideoOutput> result = nullptr;

    int32_t retCode = CAMERA_OK;

    camera_format_t metaFormat;

    metaFormat = GetCameraMetadataFormat(profile.GetCameraFormat());

    retCode = serviceProxy_->CreateVideoOutput(surface->GetProducer(), metaFormat,

                                               profile.GetSize().width, profile.GetSize().height, streamRepeat);

    if (retCode == CAMERA_OK) {

        result = new(std::nothrow) VideoOutput(streamRepeat);

        if (result == nullptr) {

            MEDIA_ERR_LOG("Failed to new VideoOutput");

        } else {

            std::vector<int32_t> videoFrameRates = profile.GetFrameRates();

            if (videoFrameRates.size() >= 2) { // vaild frame rate range length is 2

                result->SetFrameRateRange(videoFrameRates[0], videoFrameRates[1]);

            }

            POWERMGR_SYSEVENT_CAMERA_CONFIG(VIDEO,

                                            profile.GetSize().width,

                                            profile.GetSize().height);

        }

    } else {

        MEDIA_ERR_LOG("VideoOutpout: Failed to get stream repeat object from hcamera service! %{public}d", retCode);

    }

    return result;

}

该方法中通过IPC的调用最终调用到了HCameraService的CreateVideoOutput(surface->GetProducer(), format, streamRepeat)。

sptr<VideoOutput> CameraManager::CreateVideoOutput(VideoProfile &profile, sptr<Surface> &surface)

{

    CAMERA_SYNC_TRACE;

    sptr<IStreamRepeat> streamRepeat = nullptr;

    sptr<VideoOutput> result = nullptr;

    int32_t retCode = CAMERA_OK;

    camera_format_t metaFormat;

    metaFormat = GetCameraMetadataFormat(profile.GetCameraFormat());

    retCode = serviceProxy_->CreateVideoOutput(surface->GetProducer(), metaFormat,

                                               profile.GetSize().width, profile.GetSize().height, streamRepeat);

    if (retCode == CAMERA_OK) {

        result = new(std::nothrow) VideoOutput(streamRepeat);

        if (result == nullptr) {

            MEDIA_ERR_LOG("Failed to new VideoOutput");

        } else {

            std::vector<int32_t> videoFrameRates = profile.GetFrameRates();

            if (videoFrameRates.size() >= 2) { // vaild frame rate range length is 2

                result->SetFrameRateRange(videoFrameRates[0], videoFrameRates[1]);

            }

            POWERMGR_SYSEVENT_CAMERA_CONFIG(VIDEO,

                                            profile.GetSize().width,

                                            profile.GetSize().height);

        }

    } else {

        MEDIA_ERR_LOG("VideoOutpout: Failed to get stream repeat object from hcamera service! %{public}d", retCode);

    }

    return result;

}

HCameraService的CreateVideoOutput方法中主要创建了HStreamRepeat，并且通过参数传递给前面的CameraManager使用，CameraManager通过传递的HStreamRepeat对象，进行封装，创建出VideoOutput对象。

10. 添加videoOutput到采集会话中，并且提交采集会话

该步骤类似添加CameraInput到采集会话的过程，可以参考前面的流程。

11. 开始录制

通过调用VideoOutput的Start进行录制的操作。

int32_t VideoOutput::Start()

{

    return static_cast<IStreamRepeat *>(GetStream().GetRefPtr())->Start();

}

该方法中会调用到HStreamRepeat的Start方法。

int32_t HStreamRepeat::Start()

{

    CAMERA_SYNC_TRACE;

    if (streamOperator_ == nullptr) {

        return CAMERA_INVALID_STATE;

    }

    if (curCaptureID_ != 0) {

        MEDIA_ERR_LOG("HStreamRepeat::Start, Already started with captureID: %{public}d", curCaptureID_);

        return CAMERA_INVALID_STATE;

    }

    int32_t ret = AllocateCaptureId(curCaptureID_);

    if (ret != CAMERA_OK) {

        MEDIA_ERR_LOG("HStreamRepeat::Start Failed to allocate a captureId");

        return ret;

    }

    std::vector<uint8_t> ability;

    OHOS::Camera::MetadataUtils::ConvertMetadataToVec(cameraAbility_, ability);

    CaptureInfo captureInfo;

    captureInfo.streamIds_ = {streamId_};

    captureInfo.captureSetting_ = ability;

    captureInfo.enableShutterCallback_ = false;

    MEDIA_INFO_LOG("HStreamRepeat::Start Starting with capture ID: %{public}d", curCaptureID_);

    CamRetCode rc = (CamRetCode)(streamOperator_->Capture(curCaptureID_, captureInfo, true));

    if (rc != HDI::Camera::V1_0::NO_ERROR) {

        ReleaseCaptureId(curCaptureID_);

        curCaptureID_ = 0;

        MEDIA_ERR_LOG("HStreamRepeat::Start Failed with error Code:%{public}d", rc);

        ret = HdiToServiceError(rc);

    }

    return ret;

}

核心的代码是streamOperator_->Capture，其中最后一个参数true，表示采集连续数据。

12. 录制结束，保存录制文件

六、总结

本文主要对OpenHarmony 3.2 Beta多媒体子系统的视频录制进行介绍，首先梳理了整体的录制流程，然后对录制过程中的主要步骤进行了详细地分析。视频录制主要分为以下几个步骤：

（1）获取CameraManager实例。

（2）创建采集会话CaptureSession。

（3）创建CameraInput实例，并且将输入设备添加到CaptureSession中。

（4）创建Video录制需要的Surface。

（5）创建VideoOutput实例，并且将输出添加到CaptureSession中。

（6）提交采集会话的配置。

（7）调用VideoOutput的Start方法，进行视频的录制。

（8）录制结束，保存录制的文件。

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