本主題是教學課程的步驟 1,如何使用 Media Foundation播放媒體檔案。 完整的程式代碼列在 媒體工作階段播放範例主題中,。
在本教學課程中,播放功能會封裝在 CPlayer
類別中。
CPlayer
類別宣告如下:
const UINT WM_APP_PLAYER_EVENT = WM_APP + 1;
// WPARAM = IMFMediaEvent*, WPARAM = MediaEventType
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.
};
class CPlayer : public IMFAsyncCallback
{
public:
static HRESULT CreateInstance(HWND hVideo, HWND hEvent, CPlayer **ppPlayer);
// IUnknown methods
STDMETHODIMP QueryInterface(REFIID iid, void** ppv);
STDMETHODIMP_(ULONG) AddRef();
STDMETHODIMP_(ULONG) Release();
// IMFAsyncCallback methods
STDMETHODIMP GetParameters(DWORD*, DWORD*)
{
// Implementation of this method is optional.
return E_NOTIMPL;
}
STDMETHODIMP Invoke(IMFAsyncResult* pAsyncResult);
// Playback
HRESULT OpenURL(const WCHAR *sURL);
HRESULT Play();
HRESULT Pause();
HRESULT Stop();
HRESULT Shutdown();
HRESULT HandleEvent(UINT_PTR pUnkPtr);
PlayerState GetState() const { return m_state; }
// Video functionality
HRESULT Repaint();
HRESULT ResizeVideo(WORD width, WORD height);
BOOL HasVideo() const { return (m_pVideoDisplay != NULL); }
protected:
// Constructor is private. Use static CreateInstance method to instantiate.
CPlayer(HWND hVideo, HWND hEvent);
// Destructor is private. Caller should call Release.
virtual ~CPlayer();
HRESULT Initialize();
HRESULT CreateSession();
HRESULT CloseSession();
HRESULT StartPlayback();
// Media event handlers
virtual HRESULT OnTopologyStatus(IMFMediaEvent *pEvent);
virtual HRESULT OnPresentationEnded(IMFMediaEvent *pEvent);
virtual HRESULT OnNewPresentation(IMFMediaEvent *pEvent);
// Override to handle additional session events.
virtual HRESULT OnSessionEvent(IMFMediaEvent*, MediaEventType)
{
return S_OK;
}
protected:
long m_nRefCount; // Reference count.
IMFMediaSession *m_pSession;
IMFMediaSource *m_pSource;
IMFVideoDisplayControl *m_pVideoDisplay;
HWND m_hwndVideo; // Video window.
HWND m_hwndEvent; // App window to receive events.
PlayerState m_state; // Current state of the media session.
HANDLE m_hCloseEvent; // Event to wait on while closing.
};
以下是有關 CPlayer
的一些注意事項:
- 常數 WM_APP_PLAYER_EVENT 會定義私人視窗訊息。 此訊息可用來通知應用程式媒體會話事件。 請參閱 步驟 5:處理媒體會話事件。
-
PlayerState
列舉會定義CPlayer
物件的可能狀態。 -
CPlayer
類別會實作 IMFAsyncCallback 介面,用來從媒體會話取得事件通知。 -
CPlayer
建構函式是私有的。 應用程式會呼叫靜態CreateInstance
方法來建立CPlayer
類別的實例。 -
CPlayer
解構函式也是私有的。CPlayer
類別會實作 IUnknown ,因此物件的存留期會透過其參考計數來控制(m_nRefCount)。 若要終結物件,應用程式會呼叫 IUnknown::Release,而不是 刪除。 -
CPlayer
物件會同時管理媒體會話和媒體來源。
實作 IUnknown
CPlayer
類別會實作 IMFAsyncCallback,其繼承 IUnknown。
此處顯示的程式代碼是一個相當標準的 IUnknown實作。 如果您想要的話,您可以使用 Active Template Library (ATL) 來實作這些方法。 不過,CPlayer
不支援 CoCreateInstance 或任何進階 COM 功能,因此這裡沒有壓倒性的理由可以使用 ATL。
HRESULT CPlayer::QueryInterface(REFIID riid, void** ppv)
{
static const QITAB qit[] =
{
QITABENT(CPlayer, IMFAsyncCallback),
{ 0 }
};
return QISearch(this, qit, riid, ppv);
}
ULONG CPlayer::AddRef()
{
return InterlockedIncrement(&m_nRefCount);
}
ULONG CPlayer::Release()
{
ULONG uCount = InterlockedDecrement(&m_nRefCount);
if (uCount == 0)
{
delete this;
}
return uCount;
}
相關主題
-
如何使用 Media Foundation 播放媒體檔案