【Media Foundation】简单实例 - 使用Media Session来播放文件

参考MSDN官方的页面：http://msdn.microsoft.com/en-us/library/ms703190(v=vs.85)

本文详细演示了如何使用Media Foundation中的Media Session对象来播放媒体文件。也就是不自己编写/自定义任何的Media Foundation组件，一切都是用现成的，以及让Media Foundation“自动完成”的（如Topology的解析）。Media Foundation的API会根据文件的路径或URL智能创建合适的media source组件，并会智能地在media source和音视频渲染器(renderer)之间添加合适的解码器等等。Topology中的数据流等任务由Media Session来处理。

这是最简单的开发任务。然而，如果要实现使用自定义的meida source或media transform组件这样的任务，可能不能使用Media Session。

 

 

预备知识

 

在阅读本主题之前，你需要熟悉以下MF概念：

• Media Session
• Source Resolver
• Topologies
• Media Event Generators
• Presentation Descriptors

注意：此主题不描述如何播放被DRM保护的文件。关于MMF中DRM的相关信息，见 How to Play Protected Media Files。

其实不太了解以上概念也没关系，通过这个小例子的动手实践，我们会对一些基本概念有个基本了解。

 

概述

以下对象用来和Media Session播放多媒体文件：

• media source对象用来解析多媒体文件或其他媒体数据源。media source为文件中的每个音频或视频流创建一个steam对象。 Decoders把编码后的多媒体数据转换为非压缩视频和音频
• Source Resolver从URL创建一个media source
• EVR将视频渲染到屏幕上
• SAR将音频渲染至扬声器或其他音频输出设备
• Topology定义从media source至EVR和SAR的数据流
• Media Session控制数据流，并发送状态数据到应用程序。下图展示了这个过程

 

 

step by step实例

大概了解一下概念，我们可以来进行实践了。我们主要将完成以下任务：

• Media Foundation平台的初始化与关闭
• 创建media session
• 根据文件路径，（智能）创建（合适的）media source
• 创建topology，添加media source、EVR/SAR（renderer）节点，并将其连接，此时的topology是一个partial topology
• 将刚创建的topology关联到media session，内部的topology loader会给partial topology“智能地”加入所需的解码器等节点，使其成为一个complete topology
• 获取和处理来自media session的事件
• 用media session来控制播放，但不要直接操作media source
• 程序结束，释放资源

1. 创建程序

我使用visual studio 2012创建了一个基于对话框的MFC项目。含有可缩放的边框、 最小化框。

再创建一个菜单，把对话框的菜单属性设为此菜单。

添加全局的播放核心类对象

Core*  　　g_pCore = NULL; 

Core* 　　_pCore = NULL;

在stdafx.h中添加要用到的头文件和类模板。头文件后面的注释说明了为什么需要它

#include <mfapi.h>    // MFStartup, mfplat.lib
#include <mfidl.h>    // MFCreateMediaSession, mf.lib
#include <evr.h>  // IMFVideoDisplayControl, strmiids.lib
#include <shlwapi.h>  // QITABENT, shlwapi.lib
#include <mferror.h>  // MF_E_ALREADY_INITIALIZED

template <class T> void SafeRelease(T **ppT)
{
    if (*ppT)
    {
        (*ppT)->Release();
        *ppT = NULL;
    }
}

#include "Core.h" // Core类头文件

配置项目属性，此项目需要链接以下Lib:

mfplat.lib; mf.lib; mfuuid.lib; strmiids.lib; shlwapi.lib 

mfplat.lib; mf.lib; mfuuid.lib; strmiids.lib; shlwapi.lib

 

2. 创建播放核心类Core

首先定义播放事件标识和播放状态的枚举

constUINT WM_APP_PLAYER_EVENT = WM_APP + 1;


enum PlayerState
{
    Closed = 0,     // No session.
    Ready,          // Session was created, ready to open a file.
    OpenPending,    // Session is opening a file.
    Started,        // Session is playing a file.
    Paused,         // Session is paused.
    Stopped,        // Session is stopped (ready to play).
    Closing         // Application has closed the session,
                    // but is waiting for MESessionClosed.
};

 

此类被设计为单例模式（singleton），为了处理事件方便，它继承自IMFAsyncCallback接口，此接口又继承自IUnknown接口。因此我们要为Core类实现这些接口的所有必需方法。

类声明：

class Core : public IMFAsyncCallback
{
protected:
    Core(HWND hVideo);
    virtual ~Core(void);

public:
    staticHRESULT CreateInstance(HWND hVideo, Core** ppCore);

    // IUnknown方法
    STDMETHODIMP QueryInterface(REFIID iid, void** ppv);
    STDMETHODIMP_(ULONG) AddRef();
    STDMETHODIMP_(ULONG) Release();
    // IMFAsyncCallback方法
    STDMETHODIMP GetParameters(DWORD*, DWORD*)
    { return E_NOTIMPL;}
    STDMETHODIMP Invoke(IMFAsyncResult* pAsyncResult);

    HRESULT Initialize();
    HRESULT OpenFile(PCWSTR sURL);
    HRESULT HandleEvent(UINT_PTR pEvent);
    PlayerState GetState() const { return m_state; }
    BOOL    HasVideo() const { return (m_pVideoControl != NULL); }

    HRESULT StartPlay();
    HRESULT Play();
    HRESULT Pause();
    HRESULT Stop();
    HRESULT Shutdown();
    HRESULT Repaint();
    HRESULT ResizeVideo(WORD width, WORD height);

    HRESULT OnTopologyStatus(IMFMediaEvent*);
    HRESULT OnPresentationEnded(IMFMediaEvent*);

private:
    long                    m_nRefCount;
    PlayerState             m_state;
    IMFMediaSession*        m_pMediaSession;
    IMFMediaSource*         m_pMediaSource;
    IMFVideoDisplayControl* m_pVideoControl;
    HWND                    m_hwndVideo;
    HANDLE                  m_hCloseEvent;
};   virtual ~Core(void); public: static HRESULT CreateInstance(HWND hVideo, Core** ppCore); // IUnknown方法 STDMETHODIMP QueryInterface(REFIID iid, void** ppv); STDMETHODIMP_(ULONG) AddRef(); STDMETHODIMP_(ULONG) Release(); // IMFAsyncCallback方法 STDMETHODIMP GetParameters(DWORD*, DWORD*) { return E_NOTIMPL;} STDMETHODIMP Invoke(IMFAsyncResult* pAsyncResult); HRESULT Initialize(); HRESULT OpenFile(PCWSTR sURL); HRESULT HandleEvent(UINT_PTR pEvent); PlayerState GetState() const { return m_state; } BOOL HasVideo() const { return (m_pVideoControl != NULL); } HRESULT StartPlay(); HRESULT Play(); HRESULT Pause(); HRESULT Stop(); HRESULT Shutdown(); HRESULT Repaint(); HRESULT ResizeVideo(WORD width, WORD height); HRESULT OnTopologyStatus(IMFMediaEvent*); HRESULT OnPresentationEnded(IMFMediaEvent*); private: long m_nRefCount; PlayerState m_state; IMFMediaSession* m_pMediaSession; IMFMediaSource* m_pMediaSource; IMFVideoDisplayControl* m_pVideoControl; HWND m_hwndVideo; HANDLE m_hCloseEvent; };

构造函数、接口以及初始化等函数的实现， Event句柄m_hCloseEvent用来设置播放关闭时的标志，m_hwndVideo就是播放用的视频窗口，我设为主对话框的客户窗口，m_pVideoControl是一个IMFVideoDisplayControl接口指针，用来完成播放窗口相关的控制，如调整尺寸和重绘：

Core::Core(HWND hVideo) :
    m_pMediaSession(NULL),
    m_pMediaSource(NULL),
    m_pVideoControl(NULL),
    m_hwndVideo(hVideo),
    m_hCloseEvent(NULL),
    m_state(Closed),
    m_nRefCount(1)
{
}


Core::~Core(void)
{
    if(m_pMediaSession)
    {
        Shutdown();
    }
}

HRESULT Core::QueryInterface(REFIID riid, void** ppv)
{
    staticconst QITAB qit[] =
    {
        QITABENT(Core, IMFAsyncCallback),
        { 0 }
    };
    return QISearch(this, qit, riid, ppv);
}

ULONG Core::AddRef()
{
    return InterlockedIncrement(&m_nRefCount);
}

ULONG Core::Release()
{
    ULONG uCount = InterlockedDecrement(&m_nRefCount);
    if(uCount == 0)
        deletethis;
    return uCount;
}


HRESULT Core::CreateInstance(HWND hVideo, Core** ppCore)
{
    if(hVideo == NULL)  return E_UNEXPECTED;
    if(ppCore == NULL)  return E_POINTER;

    Core* pCore = new Core(hVideo);
    if(pCore == NULL)   return E_OUTOFMEMORY;

    HRESULT hr = pCore->Initialize();
    if(SUCCEEDED(hr))
    {
        *ppCore = pCore;
        (*ppCore)->AddRef();
    }

    SafeRelease(&pCore);
    return hr;
}

HRESULT Core::Initialize()
{
    if(m_hCloseEvent)
        return MF_E_ALREADY_INITIALIZED;

    HRESULT hr = MFStartup(MF_VERSION);
    if(FAILED(hr))  return hr;

    m_hCloseEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
    if(m_hCloseEvent == NULL)
        hr = HRESULT_FROM_WIN32(GetLastError());

    return hr;
}

3. 打开文件时的处理

这是一个核心的部分，代码较多，为了简单，我把所有代码都写到一个函数里去了，主要是为了理解方便。 主要完成了以下工作：

• 创建media session
• 开始从media session取得事件，开启播放相关事件的流动
• 根据文件路径创建合适的media source
• 创建partial topology
• 为media source的各个选定(selected)流创建source节点和renderer节点，将它们添加到partial topology并相互连接
• 将partial topology与media session关联，将partial topology解析成完整可用的topology

HRESULT Core::OpenFile(PCWSTR sURL)
{
    assert(m_state == Closed || m_state == Stopped);

    // 创建Media Session
    HRESULT hr = MFCreateMediaSession(NULL, &m_pMediaSession);
    if(FAILED(hr))  return hr;
    m_state = Ready;
    // 开始从Media Session取得事件
    hr = m_pMediaSession->BeginGetEvent((IMFAsyncCallback*)this, NULL);
    if(FAILED(hr))  return hr;


    // 创建Media Source
    IMFSourceResolver* pSourceResolver = NULL;
    IUnknown* pUnknown = NULL;
    IMFTopology* pTopology = NULL;
    IMFPresentationDescriptor* pPD = NULL;

    MF_OBJECT_TYPE objType = MF_OBJECT_INVALID;
    SafeRelease(&m_pMediaSource);

    hr = MFCreateSourceResolver(&pSourceResolver);
    if(FAILED(hr))  goto over;

    // 为简单，弄成同步方法
    hr = pSourceResolver->CreateObjectFromURL(
        sURL,
        MF_RESOLUTION_MEDIASOURCE,
        NULL,
        &objType,
        &pUnknown);
    if(FAILED(hr))  goto over;

    hr = pUnknown->QueryInterface(IID_PPV_ARGS(&m_pMediaSource));
    if(FAILED(hr))  goto over;


    // 创建Topology
    assert(m_pMediaSession != NULL);
    assert(m_pMediaSource != NULL);

    DWORD cStreams = 0;

    hr = MFCreateTopology(&pTopology);
    if(FAILED(hr))  goto over;

    // 创建PresentationDescriptor
    hr = m_pMediaSource->CreatePresentationDescriptor(&pPD);
    if(FAILED(hr))  goto over;

    // 获取source中的stream数目
    hr = pPD->GetStreamDescriptorCount(&cStreams);
    if(FAILED(hr))  goto over;

    assert(pTopology != NULL);
    // 为每个stream创建topology节点，并将其加入到topology
    for(DWORD i = 0; i<cStreams; i++ )
    {
            IMFStreamDescriptor* pSD = NULL;
        IMFTopologyNode* pSourceNode = NULL;
        IMFTopologyNode* pOutputNode = NULL;
        BOOL bSelected = FALSE;

        hr= pPD->GetStreamDescriptorByIndex(i, &bSelected, &pSD);
        if(FAILED(hr)) goto over2;
        if(bSelected)
        {
            // source node
            hr = MFCreateTopologyNode(MF_TOPOLOGY_SOURCESTREAM_NODE, &pSourceNode);
            if(FAILED(hr))  goto over2;
            hr = pSourceNode->SetUnknown(MF_TOPONODE_SOURCE, m_pMediaSource);
            if(FAILED(hr))  goto over2;
            hr = pSourceNode->SetUnknown(MF_TOPONODE_PRESENTATION_DESCRIPTOR, pPD);
            if(FAILED(hr))  goto over2;
            hr = pSourceNode->SetUnknown(MF_TOPONODE_STREAM_DESCRIPTOR, pSD);
            if(FAILED(hr))  goto over2;

            // output node
            IMFMediaTypeHandler* pHandler = NULL;
            IMFActivate* pRendererActivate = NULL;
            GUID guidMajorType = GUID_NULL;
            DWORD id = 0;

            pSD->GetStreamIdentifier(&id); // 忽略错误
            hr = pSD->GetMediaTypeHandler(&pHandler);
            if(FAILED(hr))  goto over3;
            hr = pHandler->GetMajorType(&guidMajorType);
            if(FAILED(hr))  goto over3;
            hr = MFCreateTopologyNode(MF_TOPOLOGY_OUTPUT_NODE, &pOutputNode);
            if(FAILED(hr))  goto over3;
            if(MFMediaType_Audio == guidMajorType)
                hr = MFCreateAudioRendererActivate(&pRendererActivate);
            elseif(MFMediaType_Video == guidMajorType)
                hr = MFCreateVideoRendererActivate(m_hwndVideo, &pRendererActivate);
            else
                hr = E_FAIL;
            if(FAILED(hr))  goto over3;
            hr = pOutputNode->SetObject(pRendererActivate);
            if(FAILED(hr))  goto over3;

            // 把source节点和输出节点添加到topology，并连接它们
            hr = pTopology->AddNode(pSourceNode);
            if(FAILED(hr))  goto over3;
            hr = pTopology->AddNode(pOutputNode);
            if(FAILED(hr))  goto over3;
            hr = pSourceNode->ConnectOutput(0, pOutputNode, 0);
over3:
            SafeRelease(&pRendererActivate);
            SafeRelease(&pHandler);
            goto over2;
        }

over2:
        SafeRelease(&pSD);
        SafeRelease(&pSourceNode);
        SafeRelease(&pOutputNode);
    }

    hr = m_pMediaSession->SetTopology(0, pTopology);
    if(FAILED(hr))  goto over;
    m_state = OpenPending;

over:
    if(FAILED(hr))  m_state = Closed;

    SafeRelease(&pPD);
    SafeRelease(&pTopology);
    SafeRelease(&pSourceResolver);
    SafeRelease(&pUnknown);
    return hr;
}

 主对话框需要提供一个文件/打开菜单，用来打开文件，它的响应如下。由于IMFSourceResolver::CreateObjectFromURL方法只支持LPCWSTR类型的文件路径字符串参数，所以当我们以多字节配置build程序时，需要添加代码，把打开文件对话框取得的多字节文件路径字符串转换成宽字符串。

void CBlackPlayerDlg::OnOpen()
{
    HRESULT hr = S_OK;

    TCHAR path[MAX_PATH];
    path[0] = _T('\0');

    OPENFILENAME ofn;
    ::ZeroMemory(&ofn, sizeof(ofn));
    ofn.lStructSize = sizeof(ofn);
    ofn.hwndOwner = this->GetSafeHwnd();
    ofn.lpstrFilter = _T("Media Files\0*.asf;*.avi;*.mp3;")
                          _T("*.mp4;*.wav;*.wma;*.wmv\0All files\0*.*\0");
    ofn.lpstrFile = path;
    ofn.nMaxFile = MAX_PATH;
    ofn.Flags = OFN_FILEMUSTEXIST;
    ofn.hInstance = AfxGetInstanceHandle();

    if(::GetOpenFileName(&ofn))
    {
#ifdef UNICODE
        hr = g_pCore->OpenFile(ofn.lpstrFile);
#else
        size_t cLen = 0, cChars = 0;
        cLen = _tcslen(ofn.lpstrFile);
        WCHAR wstr[MAX_PATH*2] = {L'\0'};

        ::MultiByteToWideChar(CP_ACP, 0, ofn.lpstrFile, -1, (LPWSTR)wstr, MAX_PATH);
        hr = g_pCore->OpenFile(wstr);
#endif
        if(SUCCEEDED(hr))
        {
            UpdateUI(g_pCore->GetState());
        }
        else
        {
            AfxMessageBox(_T("无法打开文件！"));
        }
    }
}

4. 处理media session事件

第3步代码的开头我们已经使用BeginGetEvent方法开始获取Media Session的事件，这是一个异步方法，当下一个事件发生时，media session会调用IMFAsyncCallback::Invoke方法。注意此方法是在worker线程调用的，不是主程序所在线程，所以这方法必须线程安全。

HRESULT Core::Invoke(IMFAsyncResult* pResult)
{
    MediaEventType meType = MEUnknown;
    IMFMediaEvent* pEvent = NULL;

    // 从事件队列中获取事件
    HRESULT hr = m_pMediaSession->EndGetEvent(pResult, &pEvent);
    if(FAILED(hr))  goto over;
    // 取得事件的类型
    hr = pEvent->GetType(&meType);
    if(FAILED(hr))  goto over;

    if(meType == MESessionClosed)
    {
        ::SetEvent(m_hCloseEvent);
    }
    else
    {
        hr = m_pMediaSession->BeginGetEvent(this, NULL);
        if(FAILED(hr))  goto over;
    }

    if(m_state != Closing)
    {
        pEvent->AddRef();
        ::PostMessage(m_hwndVideo, WM_APP_PLAYER_EVENT, (WPARAM)pEvent, (LPARAM)0);
    }

over:
    SafeRelease(&pEvent);
    return S_OK;
}

Invoke方法中，我们先用EndGetEvent取得事件，接着用PostMessage将此事件发送给主程序窗口，其实主窗口还是把它送回给了Core的HandleEvent方法来进行实际处理。还要再次调用BeginGetEvent方法来异步获取下一事件。所以主对话框类要添加WM_APP_PLAYER_EVENT事件的处理程序：

afx_msg LRESULT CBlackPlayerDlg::OnPlayerEvent(WPARAM wParam, LPARAM lParam)
{
    HRESULT hr = S_OK;
    hr = g_pCore->HandleEvent(wParam);
    if(FAILED(hr))
        AfxMessageBox(_T("事件处理发生错误！"));

    UpdateUI(g_pCore->GetState());
    return 0;
}

以下是Core类的HandleEvent，还可以根据需要添加更多的事件处理：

HRESULT Core::HandleEvent(UINT_PTR pEventPtr)
{
    HRESULT hrStatus = S_OK;
    HRESULT hr = E_FAIL;
    IMFMediaEvent* pEvent = NULL;

    IUnknown* pUnk = (IUnknown*)pEventPtr;
    if(pUnk == NULL)    return E_POINTER;
    hr = pUnk->QueryInterface(IID_PPV_ARGS(&pEvent));
    if(FAILED(hr))  goto over;

    MediaEventType meType = MEUnknown;
    hr = pEvent->GetType(&meType);
    if(FAILED(hr))  goto over;

    hr = pEvent->GetStatus(&hrStatus);
    if(FAILED(hr))  goto over;
    if(FAILED(hrStatus))
    {
        hr = hrStatus;
        goto over;
    }

    switch(meType)
    {
    case MESessionTopologyStatus:
        hr = OnTopologyStatus(pEvent);
        break;
    case MEEndOfPresentation:
        hr = OnPresentationEnded(pEvent);
        break;
    default:
        break;
    }

over:
    SafeRelease(&pUnk);
    SafeRelease(&pEvent);
    return hr;
}

相关的具体事件的处理方法 ：

HRESULT Core::OnTopologyStatus(IMFMediaEvent* pEvent)
{
    MF_TOPOSTATUS status;
    HRESULT hr = pEvent->GetUINT32(MF_EVENT_TOPOLOGY_STATUS, (UINT32*)&status);
    if(SUCCEEDED(hr) && (status == MF_TOPOSTATUS_READY))
    {
        SafeRelease(&m_pVideoControl);
        // 如果source没有视频stream，此方法将失败
        (void)MFGetService(m_pMediaSession, MR_VIDEO_RENDER_SERVICE,
            IID_PPV_ARGS(&m_pVideoControl));

        hr = StartPlay();
    }
    return hr;
}



HRESULT Core::OnPresentationEnded(IMFMediaEvent* pEvent)
{
    m_state = Stopped;
    return S_OK;
}

5. 控制播放

构建好完整的topology、设置好事件处理之后，可以真正地开始播放了，以下是播放的一些相关代码：

// 从当前位置开始播放
HRESULT Core::StartPlay()
{
    PROPVARIANT varStart;
    PropVariantInit(&varStart);
    varStart.vt = VT_EMPTY;

    // start是异步方法
    HRESULT hr = m_pMediaSession->Start(&GUID_NULL, &varStart);
    if(SUCCEEDED(hr))
        m_state = Started;
    PropVariantClear(&varStart);

    return hr;
}

HRESULT Core::Play()
{
    if(m_state != Paused && m_state != Stopped)
        return INET_E_INVALID_REQUEST;
    if(m_pMediaSession == NULL || m_pMediaSource == NULL)
        return E_UNEXPECTED;
    return StartPlay();
}

HRESULT Core::Pause()
{
    if(m_state != Started)
        return INET_E_INVALID_REQUEST;
    if(m_pMediaSession == NULL || m_pMediaSource == NULL)
        return E_UNEXPECTED;

    HRESULT hr = m_pMediaSession->Pause();
    if(SUCCEEDED(hr))
        m_state = Paused;
    return hr;
}

HRESULT Core::Stop()
{
    if(m_state != Started && m_state != Paused)
        return INET_E_INVALID_REQUEST;
    if(m_pMediaSession == NULL)
        return E_UNEXPECTED;

    HRESULT hr = m_pMediaSession->Stop();
    if(SUCCEEDED(hr))
        m_state = Stopped;
    return hr;
}

视频render(EVR)在我们提供的视频窗口绘制视频图象，这发生在一个工作线程，一般不需要管它。但如果播放暂停或停止时，当视频窗口接收到WM_PAINT消息时，我们必须通知EVR，方法是调用IMFVideoDisplayControl::RepaintVideo方法：

HRESULT Core::Repaint()
{
    if(m_pVideoControl)
        return m_pVideoControl->RepaintVideo();
    else
        return S_OK;
}

同时，我们还需要修改主对话框的OnPaint事件处理函数：

void CBlackPlayerDlg::OnPaint()
{
    if (IsIconic())
    {
        // 略。。。。
    }
    else
    {
        if(g_pCore && g_pCore->HasVideo())
            g_pCore->Repaint();

        CDialogEx::OnPaint();
    }
}

我们还需要让用户可以调整视频窗口大小，这通过IMFVideoDisplayControl::SetVideoPostition方法来完成：

HRESULT Core::ResizeVideo(WORD width, WORD height)
{
    if(m_pVideoControl)
    {
        RECT rc = {0, 0, width, height};
        return m_pVideoControl->SetVideoPosition(NULL, &rc);
    }
    else
        return S_OK;
}

类似与重绘，我们也要相应修改主对话框类，为其添加WM_SIZE的消息处理程序：

void CBlackPlayerDlg::OnSize(UINT nType, int cx, int cy)
{
    CDialogEx::OnSize(nType, cx, cy);
    if(g_pCore != NULL && g_pCore->HasVideo())
        g_pCore->ResizeVideo(cx, cy);
}

 6. 结束后的清理

 

播放完成后我们需要做一些清理工作，比如析构函数中的ShutDown方法：

HRESULT Core::Shutdown()
{
    HRESULT hr = S_OK;

    SafeRelease(&m_pVideoControl);

    if(m_pMediaSession)
    {
        DWORD dwRet = 0;
        m_state = Closing;
        hr = m_pMediaSession->Close();
        if(FAILED(hr))  goto over;

        dwRet = WaitForSingleObject(m_hCloseEvent, 3000);
    }

    // 以下shutdown都是同步方法，无事件
    if(m_pMediaSource)
        m_pMediaSource->Shutdown();
    if(m_pMediaSession)
        m_pMediaSession->Shutdown();

    SafeRelease(&m_pMediaSource);
    SafeRelease(&m_pMediaSession);
    m_state = Closed;

    MFShutdown();
    if(m_hCloseEvent)
    {
        ::CloseHandle(m_hCloseEvent);
        m_hCloseEvent = NULL;
    }

over:
    return hr;
}

我在对话框类的析构函数里添加：

CBlackPlayerDlg::~CBlackPlayerDlg()
{
    if(g_pCore != NULL)
    {
        g_pCore->Shutdown();
        g_pCore->Release();
    }
}

7. 杂项

如果要用键盘的空格键控制视频的暂停/重新播放，主对话框类需要重载PreTranslateMessage函数：

 

// 必须直接重载此函数，直接处理WM_CHAR或WM_KEYUP消息不行
BOOL CBlackPlayerDlg::PreTranslateMessage(MSG* pMsg)
{
    // TODO: 在此添加专用代码和/或调用基类
    if(g_pCore != NULL && pMsg->message == WM_KEYUP)
    {
        if(pMsg->wParam == VK_SPACE)
        {
            if(g_pCore->GetState() == Started)
                g_pCore->Pause();
            elseif(g_pCore->GetState() == Paused)
                g_pCore->Play();
        }
        return TRUE;
    }

    return CDialogEx::PreTranslateMessage(pMsg);
}

如果要添加个控制菜单，里面有暂停、停止，它们的响应如下：

void CBlackPlayerDlg::OnPause()
{
    if(g_pCore != NULL)
    {
        if(g_pCore->GetState() == Started)
                g_pCore->Pause();
    }
}


void CBlackPlayerDlg::OnStop()
{
    if(g_pCore != NULL)
    {
        if(g_pCore->GetState() == Started || g_pCore->GetState() == Paused)
            g_pCore->Stop();
    }
}