由于AVI格式是微软推出的，所以在Windows下操作比较容易，这里我用DirectShow读写AVI视频文件，并把所有操作封装成一个类：AVICodec。下面是类的定义：

class AVICodec
{
public:
AVICodec(){size = -1;}
AVICodec(LPCWSTR avifile);
void release();
int init_getframe();
char* getframe(unsigned int index);
int getFrame(unsigned int index);
int getFrameEnd();
void play();
private:
IGraphBuilder *pGraph;
IMediaControl *pControl;
IMediaEvent   *pEvent;
IMediaDet   *pDet;

AM_MEDIA_TYPE amMediaType;
public:
BITMAPINFOHEADER *pbih;
double fps, length;
unsigned int nFrame;
long size;
bool is_begin;
char * pBuffer;
private:
char * buf;
};

这个类目前实现两个功能：

1. 播放AVI文件      play()
2. 获取指定帧的数据，返回数据是RGB24格式 GetFrame()

下面给出代码：

AVICodec::AVICodec(LPCWSTR avifile)//类初始化，avifile是文件名
{
pGraph   = NULL;
pControl = NULL;
pEvent   = NULL;
size   = -1;
is_begin = false;
buf    = NULL;
HRESULT hr = CoInitialize(NULL);
if(FAILED(hr)){
   cout<<"initialize COM Library failed"<<endl;
   exit(0);
}
hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
                        IID_IGraphBuilder, (void **)&pGraph);
if(FAILED(hr)){
   cout<<"could not create Filter Graph Manager"<<endl;
   exit(0);
}
hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
hr = pGraph->RenderFile(avifile, NULL);
if(FAILED(hr)){
   cout<<"open AVI file failed"<<endl;
   exit(0);
}
hr = CoCreateInstance(CLSID_MediaDet, NULL, CLSCTX_INPROC, IID_IMediaDet,
   (void **)&pDet);
if(FAILED(hr)){
   cout<<"initialize MediaDet Failed"<<endl;
   exit(0);
}
hr = pDet->put_Filename(BSTR(avifile));
if(FAILED(hr)){
   cout<<"MediaDet put file failed"<<endl;
   exit(0);
}
}

int AVICodec::init_getframe()//抓图的初始化，得到帧数，帧频等参数
{
long lStreams;
HRESULT hr = pDet->get_OutputStreams(&lStreams);
if(FAILED(hr)){
   cout<<"Failed : pDet->get_OutputStreams()"<<endl;
   return -1;
}

hr = pDet->put_CurrentStream(0);
if(FAILED(hr)){
   cout<<"Failed : pDet->put_CurrentStream()"<<endl;
   return -1;
}
hr = pDet->get_StreamMediaType(&amMediaType);
if(FAILED(hr)){
   cout<<"Failed : pDet->get_StreamMediaType()"<<endl;
}
pbih = &((VIDEOINFOHEADER *)amMediaType.pbFormat)->bmiHeader;
if(FAILED(pDet->get_FrameRate(&fps)) || FAILED(pDet->get_StreamLength(&length)))
{
   cout<<"Failed : pDet->get_FrameRate() || pDet->get_StreamLength()"<<endl;
   return -1;
}
nFrame = (unsigned int)(length * fps);
return 1;
}

int AVICodec::getFrame(unsigned int index)//抓取index帧的图像，存放在buf中
{
if(index>nFrame){
   cout<<"exceed max frame index"<<endl;
   return -1;
}
HRESULT hr;
double position = (double)(index*1.0/fps);

hr = pDet->GetBitmapBits(position,&size,NULL,pbih->biWidth,pbih->biHeight);
   if(FAILED(hr)){
    cout<<"Failed : pDet->GetBitmapBits()"<<endl;
    return -1;
   }
if(is_begin==false){
   buf = new char[size];
   memset(buf,0,size);
   is_begin = true;
}
//memset(buf,0,size);
hr = pDet->GetBitmapBits(position, NULL, buf, pbih->biWidth, pbih->biHeight);
BITMAPINFO *binfo = (BITMAPINFO *)buf;
pBuffer = buf + ((BITMAPINFO *)buf)->bmiHeader.biSize;
if(FAILED(hr)){
   cout<<"Failed : pDet->GetBitmapBits()"<<endl;
   return -1;
}
return 1;
}

int AVICodec::getFrameEnd()//抓图后释放内存
{
is_begin = false;
delete[] buf;
return 1;
}

void AVICodec::play()//播放AVI文件，文件名在类初始化时给定
{
HRESULT hr = pControl->Run();
if(SUCCEEDED(hr)){
   long evCode;
   pEvent->WaitForCompletion(INFINITE,&evCode);
}
}

void AVICodec::release()//运行完释放资源
{
pControl->Release();
pEvent->Release();
pControl->Release();
pDet->Release();
CoUninitialize();
}