DirectShow应用：只用API调用实现网络播放

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DirectShow应用：只用API调用实现网络播放

本文只用一个main.cpp文件就实现了简单的网络媒体播放。代码如下：

一．预定义

#define NO_SHLWAPI_STRFCNS

#include <DShow.h>

#include <atlcomcli.h>

#pragma comment(lib,"strmiids.lib")

LPCTSTR lpAppName = TEXT("An Example of Playing Internet File\(http:\\\\www.entrigle.com\\movie\\Megamind.avi) By Simply Using WindowsAPI!");

LPCTSTR lpClassName= TEXT("MY Class");

LRESULT CALLBACKWndProc( HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam );

void play( HWND hwnd );

头文件dshow.h中包含DirectShow常用的内容，altcomcli.h包含智能指针等相关内容。接下来，引用需要的库，定义回调函数及播放函数原型。

二．入口函数

int APIENTRY WinMain( HINSTANCE hinstance, HINSTANCEhPreviousInsance,

LPTSTR lpCmdLine,intnCmdShow )

{

// to setupthe properties of the window

MSG msg;

HWND hwnd;

WNDCLASS wc;

wc.style = CS_HREDRAW | CS_VREDRAW;

wc.lpfnWndProc = (WNDPROC)WndProc; // 为窗体指定回调函数

wc.cbClsExtra = 0;

wc.cbWndExtra = 0;

wc.hInstance = hinstance;

wc.hIcon = LoadIcon( hinstance,IDI_APPLICATION );

wc.hCursor = LoadCursor( hinstance,IDC_ARROW );

wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);

wc.lpszMenuName = lpAppName;

wc.lpszClassName = lpClassName;

// toregister and create the window

if(!RegisterClass( &wc ) )

{

returnFALSE;

}

hwnd = CreateWindow( lpClassName,lpAppName, WS_OVERLAPPEDWINDOW,

CW_USEDEFAULT,0,

NULL,

hinstance,

NULL

);

if(!hwnd )

{

returnFALSE;

}

ShowWindow(hwnd, nCmdShow);

UpdateWindow(hwnd);

// to playthe network file

play( hwnd );

// 进入消息循环

while(GetMessage(&msg, NULL, 0, 0 ))

{

TranslateMessage( &msg );

DispatchMessage( &msg );

}

returnmsg.wParam;

}

如上，定义Windows入口函数WinMain，首先定义窗体结构WNDCLASS变量，并通过调用RegisterClass进行注册，调用CreateWindow创建一个窗体，并激活之。然后，调用函数play播放一个网络文件。

函数play的实现代码如下：

void play( HWND hwnd )

{

// initializethe com library

HRESULT hr = CoInitializeEx( NULL,COINIT_APARTMENTTHREADED );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Initialize error!"), NULL, 0 );

return;

}

// to get thepointer for Graph Builder

CComPtr<IGraphBuilder> pGraph;

hr = CoCreateInstance(CLSID_FilterGraph, NULL,

CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void**)&pGraph );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Create Graph builder error!"), NULL, 0);

CoUninitialize();

return;

}

// to makeintelligent connection

hr = pGraph->RenderFile( L"http:\\\\\www.entrigle.com\\movie\\Megamind.avi",NULL );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Renderer file error!"), NULL, 0 );

pGraph = NULL;

CoUninitialize();

return;

}

// to get thepointer for media controlling

CComPtr<IMediaControl> pControl;

hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Create Control error!"), NULL, 0 );

pGraph = NULL;

CoUninitialize();

return;

}

// to get thepointer for media events

CComPtr<IMediaEventEx> pEvent;

hr = pGraph->QueryInterface(IID_IMediaEventEx, (void **)&pEvent );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Create Event error!"), NULL, 0 );

pGraph = NULL;

pControl = NULL;

CoUninitialize();

return;

}

// to get thepointer for video window

CComPtr<IVideoWindow> pVideo;

hr = pGraph->QueryInterface(IID_IVideoWindow, (void **)&pVideo );

if(FAILED(hr) )

{

MessageBox( NULL, TEXT("Create Video Window error!"), NULL, 0);

pGraph = NULL;

pControl = NULL;

CoUninitialize();

}

// to bind itto the window created before

pVideo->put_Owner( (OAHWND)hwnd );

RECT rect;

GetClientRect( hwnd, &rect );

pVideo->put_Left( 0 );

pVideo->put_Top( 0 );

pVideo->put_Width( rect.right -rect.left );

pVideo->put_Height( rect.bottom -rect.top );

// to playand wait

pControl->Run();

longcvCode;

pEvent->WaitForCompletion( INFINITE,&cvCode );

// to stopand release

pControl->Stop();

pVideo = NULL;

pEvent = NULL;

pControl = NULL;

pGraph = NULL;

CoUninitialize();

}

三．回调函数

回调函数只进行简单的处理，当窗口关闭时发送应用程序终止消息，当按下任意键时可重复播放。代码如下：

LRESULT CALLBACKWndProc( HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam )

{

switch(message)

{

caseWM_DESTROY :

PostQuitMessage(0);

break;

caseWM_KEYDOWN :

play( hwnd );

break;

default:

return DefWindowProc( hwnd, message, wparam, lparam);

break;

}

return0L;

}

本文旨在探索只用调用API的方式运用directshow技术，使代码量尽可能的减少，这对于Windows Api的学习和运用无疑是一个有益的尝试。