DirectShow最主要的功能就是播放视频，在这里介绍一个简单的基于DirectShow的播放器的例子，是用MFC做的，今后有机会可以基于该播放器开发更复杂的播放器软件。
注：该例子取自于《DirectShow开发指南》
首先看一眼最终结果，如图所示，播放器包含了：打开，播放，暂停，停止等功能。该图显示正在播放周杰伦的《听妈妈的话》。
迅速进入主题，看一看工程是由哪些文件组成的，如下图所示
从上图可以看出，该工程最重要的cpp文件有两个：SimplePlayerDlg.cpp和CDXGraph.cpp。前者是视频播放器对话框对应的类，而后者是对DirectShow功能进行封装的类。尤其是后面那个类，写的很好，可以说做到了“可复用”，可以移植到其他DirectShow项目中。
本文首先分析CDXGraph这个类，SimplePlayerDlg在下篇文章中再进行分析。
首先看看它的头文件：
CDXGraph.h
/* 雷霄骅
* 中国传媒大学/数字电视技术
* leixiaohua1020@126.com
*
*/
// CDXGraph.h
#ifndef __H_CDXGraph__
#define __H_CDXGraph__
// Filter graph notification to the specified window
#define WM_GRAPHNOTIFY (WM_USER+20)
class CDXGraph
{
private:
//各种DirectShow接口
IGraphBuilder * mGraph;
IMediaControl * mMediaControl;
IMediaEventEx * mEvent;
IBasicVideo * mBasicVideo;
IBasicAudio * mBasicAudio;
IVideoWindow * mVideoWindow;
IMediaSeeking * mSeeking;
DWORD mObjectTableEntry;
public:
CDXGraph();
virtual ~CDXGraph();
public:
//创建IGraphBuilder，使用CoCreateInstance
virtual bool Create(void);
//释放
virtual void Release(void);
virtual bool Attach(IGraphBuilder * inGraphBuilder);
IGraphBuilder * GetGraph(void); // Not outstanding reference count
IMediaEventEx * GetEventHandle(void);
bool ConnectFilters(IPin * inOutputPin, IPin * inInputPin, const AM_MEDIA_TYPE * inMediaType = 0);
void DisconnectFilters(IPin * inOutputPin);
bool SetDisplayWindow(HWND inWindow);
bool SetNotifyWindow(HWND inWindow);
bool ResizeVideoWindow(long inLeft, long inTop, long inWidth, long inHeight);
void HandleEvent(WPARAM inWParam, LPARAM inLParam);
//各种操作
bool Run(void); // Control filter graph
bool Stop(void);
bool Pause(void);
bool IsRunning(void); // Filter graph status
bool IsStopped(void);
bool IsPaused(void);
bool SetFullScreen(BOOL inEnabled);
bool GetFullScreen(void);
// IMediaSeeking
bool GetCurrentPosition(double * outPosition);
bool GetStopPosition(double * outPosition);
bool SetCurrentPosition(double inPosition);
bool SetStartStopPosition(double inStart, double inStop);
bool GetDuration(double * outDuration);
bool SetPlaybackRate(double inRate);
// Attention: range from -10000 to 0, and 0 is FULL_VOLUME.
bool SetAudioVolume(long inVolume);
long GetAudioVolume(void);
// Attention: range from -10000(left) to 10000(right), and 0 is both.
bool SetAudioBalance(long inBalance);
long GetAudioBalance(void);
bool RenderFile(const char * inFile);
bool SnapshotBitmap(const char * outFile);
private:
void AddToObjectTable(void) ;
void RemoveFromObjectTable(void);
//各种QueryInterface，初始各种接口
bool QueryInterfaces(void);
};
#endif // __H_CDXGraph__该头文件定义了CDXGraph类封装的各种DirectShow接口，以及提供的各种方法。在这里因为方法种类特别多，所以只能选择最关键的方法进行分析。下面打开CDXGraph.cpp看看如下几个方法吧：
Create()：用于创建IGraphBuilder
//创建IGraphBuilder，使用CoCreateInstance
bool CDXGraph::Create(void)
{
if (!mGraph)
{
if (SUCCEEDED(CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
IID_IGraphBuilder, (void **)&mGraph)))
{
AddToObjectTable();
return QueryInterfaces();
}
mGraph = 0;
}
return false;
}
需要注意的是，Create()调用了QueryInterfaces()
QueryInterfaces()：用于初始化各种接口
//各种QueryInterface，初始各种接口
bool CDXGraph::QueryInterfaces(void)
{
if (mGraph)
{
HRESULT hr = NOERROR;
hr |= mGraph->QueryInterface(IID_IMediaControl, (void **)&mMediaControl);
hr |= mGraph->QueryInterface(IID_IMediaEventEx, (void **)&mEvent);
hr |= mGraph->QueryInterface(IID_IBasicVideo, (void **)&mBasicVideo);
hr |= mGraph->QueryInterface(IID_IBasicAudio, (void **)&mBasicAudio);
hr |= mGraph->QueryInterface(IID_IVideoWindow, (void **)&mVideoWindow);
hr |= mGraph->QueryInterface(IID_IMediaSeeking, (void **)&mSeeking);
if (mSeeking)
{
mSeeking->SetTimeFormat(&TIME_FORMAT_MEDIA_TIME);
}
return SUCCEEDED(hr);
}
return false;
}Release()：释放各种接口
//释放
void CDXGraph::Release(void)
{
if (mSeeking)
{
mSeeking->Release();
mSeeking = NULL;
}
if (mMediaControl)
{
mMediaControl->Release();
mMediaControl = NULL;
}
if (mEvent)
{
mEvent->Release();
mEvent = NULL;
}
if (mBasicVideo)
{
mBasicVideo->Release();
mBasicVideo = NULL;
}
if (mBasicAudio)
{
mBasicAudio->Release();
mBasicAudio = NULL;
}
if (mVideoWindow)
{
mVideoWindow->put_Visible(OAFALSE);
mVideoWindow->put_MessageDrain((OAHWND)NULL);
mVideoWindow->put_Owner(OAHWND(0));
mVideoWindow->Release();
mVideoWindow = NULL;
}
RemoveFromObjectTable();
if (mGraph)
{
mGraph->Release();
mGraph = NULL;
}
}Run()：播放
bool CDXGraph::Run(void)
{
if (mGraph && mMediaControl)
{
if (!IsRunning())
{
if (SUCCEEDED(mMediaControl->Run()))
{
return true;
}
}
else
{
return true;
}
}
return false;
}Stop()：停止
bool CDXGraph::Stop(void)
{
if (mGraph && mMediaControl)
{
if (!IsStopped())
{
if (SUCCEEDED(mMediaControl->Stop()))
{
return true;
}
}
else
{
return true;
}
}
return false;
}
Pause()：暂停
bool CDXGraph::Pause(void)
{
if (mGraph && mMediaControl)
{
if (!IsPaused())
{
if (SUCCEEDED(mMediaControl->Pause()))
{
return true;
}
}
else
{
return true;
}
}
return false;
}SetFullScreen()：设置全屏
bool CDXGraph::SetFullScreen(BOOL inEnabled)
{
if (mVideoWindow)
{
HRESULT hr = mVideoWindow->put_FullScreenMode(inEnabled ? OATRUE : OAFALSE);
return SUCCEEDED(hr);
}
return false;
}GetDuration()：获得视频时长
bool CDXGraph::GetDuration(double * outDuration)
{
if (mSeeking)
{
__int64 length = 0;
if (SUCCEEDED(mSeeking->GetDuration(&length)))
{
*outDuration = ((double)length) / 10000000.;
return true;
}
}
return false;
}SetAudioVolume()：设置音量
bool CDXGraph::SetAudioVolume(long inVolume)
{
if (mBasicAudio)
{
HRESULT hr = mBasicAudio->put_Volume(inVolume);
return SUCCEEDED(hr);
}
return false;
}RenderFile()：关键！
bool CDXGraph::RenderFile(const char * inFile)
{
if (mGraph)
{
WCHAR szFilePath[MAX_PATH];
MultiByteToWideChar(CP_ACP, 0, inFile, -1, szFilePath, MAX_PATH);
if (SUCCEEDED(mGraph->RenderFile(szFilePath, NULL)))
{
return true;
}
}
return false;
}播放器源代码下载：http://download.csdn.net/detail/leixiaohua1020/6453467