在windowsSDK中有一个推模式的Source Filter例子，位于SDK安装目录samples\C++\Directshow\Ball下。
下面做一下简要分析：
功能：Live Source不断产生视频帧，演示在封闭围墙内碰撞的弹球的运动轨迹。使用该filter构建Filter Graph及其输出结果如下图：
类的继承结构关系为：
CBouncingBall继承自CSource
CBallStream继承自CSourceStream
可以知道，从CSource派生的Filter，它的输出Pin会使用一个数据线程，将Sample不断的推出去，具体实现如下：
//
// DoBufferProcessingLoop
//
// Grabs a buffer and calls the users processing function.
// Overridable, so that different delivery styles can be catered for.
HRESULT CSourceStream::DoBufferProcessingLoop(void) {
Command com;
OnThreadStartPlay();//开始数据传送前调用，子类可以重新实现以进行一些初始化
do {
while (!CheckRequest(&com)) {
IMediaSample *pSample;
<span style="white-space:pre"></span>//输出Pin上得到一个空的Pin
HRESULT hr = GetDeliveryBuffer(&pSample,NULL,NULL,0);
if (FAILED(hr)) {
Sleep(1);
continue;// go round again. Perhaps the error will go away
// or the allocator is decommited & we will be asked to
// exit soon.
}
// 子类必须实现的一个函数，填写Sample的实际内容
hr = FillBuffer(pSample);
if (hr == S_OK) {
hr = Deliver(pSample);//往下一个filter发送数据
pSample->Release();
// downstream filter returns S_FALSE if it wants us to
// stop or an error if it's reporting an error.
if(hr != S_OK)
{
DbgLog((LOG_TRACE, 2, TEXT("Deliver() returned %08x; stopping"), hr));
return S_OK;
}
} else if (hr == S_FALSE) {
// derived class wants us to stop pushing data
pSample->Release();
DeliverEndOfStream();
return S_OK;
} else {
// derived class encountered an error
pSample->Release();
DbgLog((LOG_ERROR, 1, TEXT("Error %08lX from FillBuffer!!!"), hr));
DeliverEndOfStream();
m_pFilter->NotifyEvent(EC_ERRORABORT, hr, 0);
return hr;
}
// all paths release the sample
}
// For all commands sent to us there must be a Reply call!
if (com == CMD_RUN || com == CMD_PAUSE) {
Reply(NOERROR);
} else if (com != CMD_STOP) {
Reply((DWORD) E_UNEXPECTED);
DbgLog((LOG_ERROR, 1, TEXT("Unexpected command!!!")));
}
} while (com != CMD_STOP);
return S_FALSE;
}
CBaseFilter的FillBuffer的实现：
<pre name="code" class="cpp">HRESULT RtpStream::FillBuffer(IMediaSample *pms)
{
CheckPointer(pms, E_POINTER);
ASSERT(m_Ball);
BYTE *pData;
long lDataLen;
pms->GetPointer(&pData);
lDataLen = pms->GetSize();
ZeroMemory(pData, lDataLen);//请屏，将图像帧设置为黑色
{
CAutoLock cAutoLockShared(&m_cSharedState);
// If we haven't just cleared the buffer delete the old
// ball and move the ball on
m_Ball->MoveBall(m_rtSampleTime - (LONG)m_iRepeatTime);
//在图像帧上画出弹球当前的位置
m_Ball->PlotBall(pData, m_BallPixel, m_iPixelSize);
// The current time is the sample's start
CRefTime rtStart = m_rtSampleTime;
// Increment to find the finish time
m_rtSampleTime += (LONG)m_iRepeatTime;
//为Sample打上时间戳
pms->SetTime((REFERENCE_TIME *)&rtStart, (REFERENCE_TIME *)&m_rtSampleTime);
}
pms->SetSyncPoint(TRUE);
return NOERROR;
}
可以看到，m_Ball是一个CBall类，主要完成弹球的位置计算以及绘制，当要在新位置上绘制弹球时，一般首先调用MoveBall
进行新位置的计算，然后调用PlotBall在计算得到的位置上绘制一个球。
下面是理解该例子的几个要点：
1.如何创建输出Pin。因为FIlter-Pin采用的是CSource-CSourceStream类结构，所以实际输出Pin的创建一般在Filter的构造函数中。
<pre name="code" class="cpp">RtpStreamFilter::RtpStreamFilter(LPUNKNOWN lpunk, HRESULT *phr) :
CSource(NAME("Rtp Source Filter"), lpunk, CLSID_BouncingBall)
{
ASSERT(phr);
CAutoLock cAutoLock(&m_cStateLock);
//首先进行内存分配，m_paStreams是一个指针数组，因为只有一个Pin，所以分配一个单元
m_paStreams = (CSourceStream **) new RtpStream*[1];
if (m_paStreams == NULL)
{
if (phr)
*phr = E_OUTOFMEMORY;
return;
}
//新生成一个CSourceStream实例
m_paStreams[0] = new RtpStream(phr, this, L"A Rtp Source Filter!");
if (m_paStreams[0] == NULL)
{
if (phr)
*phr = E_OUTOFMEMORY;
return;
}
}
2.如何在输出Pin上提供首选的媒体类型列表，包括RGB32,RGB24,RGB565,RGB555,RGB8等?如下代码描
//
// GetMediaType
//
// I _prefer_ 5 formats - 8, 16 (*2), 24 or 32 bits per pixel and
// I will suggest these with an image size of 320x240. However
// I can accept any image size which gives me some space to bounce.
//
// A bit of fun:
// 8 bit displays get red balls
// 16 bit displays get blue
// 24 bit see green
// And 32 bit see yellow
//
// Prefered types should be ordered by quality, zero as highest quality
// Therefore iPosition =
// 0 return a 32bit mediatype
// 1 return a 24bit mediatype
// 2 return 16bit RGB565
// 3 return a 16bit mediatype (rgb555)
// 4 return 8 bit palettised format
// (iPosition > 4 is invalid)
//
HRESULT RtpStream::GetMediaType(int iPosition, CMediaType *pmt)
{
CheckPointer(pmt, E_POINTER);//如果pmt为NULL，直接return
CAutoLock cAutoLock(m_pFilter->pStateLock());
if (iPosition < 0)
{
return E_INVALIDARG;
}
// Have we run off the end of types?
if (iPosition > 4)
{
return VFW_S_NO_MORE_ITEMS;
}
VIDEOINFO *pvi = (VIDEOINFO *)pmt->AllocFormatBuffer(sizeof(VIDEOINFO));
if (NULL == pvi)
return(E_OUTOFMEMORY);
ZeroMemory(pvi, sizeof(VIDEOINFO));
switch (iPosition)
{
case 0:
{
// Return our highest quality 32bit format
// since we use RGB888 (the default for 32 bit), there is
// no reason to use BI_BITFIELDS to specify the RGB
// masks. Also, not everything supports BI_BITFIELDS
SetPaletteEntries(Yellow);
pvi->bmiHeader.biCompression = BI_RGB;
pvi->bmiHeader.biBitCount = 32;
break;
}
case 1:
{ // Return our 24bit format
SetPaletteEntries(Green);
pvi->bmiHeader.biCompression = BI_RGB;
pvi->bmiHeader.biBitCount = 24;
break;
}
case 2:
{
// 16 bit per pixel RGB565
// Place the RGB masks as the first 3 doublewords in the palette area
for (int i = 0; i < 3; i++)
pvi->TrueColorInfo.dwBitMasks[i] = bits565[i];
SetPaletteEntries(Blue);
pvi->bmiHeader.biCompression = BI_BITFIELDS;
pvi->bmiHeader.biBitCount = 16;
break;
}
case 3:
{ // 16 bits per pixel RGB555
// Place the RGB masks as the first 3 doublewords in the palette area
for (int i = 0; i < 3; i++)
pvi->TrueColorInfo.dwBitMasks[i] = bits555[i];
SetPaletteEntries(Blue);
pvi->bmiHeader.biCompression = BI_BITFIELDS;
pvi->bmiHeader.biBitCount = 16;
break;
}
case 4:
{ // 8 bit palettised
SetPaletteEntries(Red);
pvi->bmiHeader.biCompression = BI_RGB;
pvi->bmiHeader.biBitCount = 8;
pvi->bmiHeader.biClrUsed = iPALETTE_COLORS;
break;
}
}
// (Adjust the parameters common to all formats...)
// put the optimal palette in place
for (int i = 0; i < iPALETTE_COLORS; i++)
{
pvi->TrueColorInfo.bmiColors[i].rgbRed = m_Palette[i].peRed;
pvi->TrueColorInfo.bmiColors[i].rgbBlue = m_Palette[i].peBlue;
pvi->TrueColorInfo.bmiColors[i].rgbGreen = m_Palette[i].peGreen;
pvi->TrueColorInfo.bmiColors[i].rgbReserved = 0;
}
pvi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pvi->bmiHeader.biWidth = m_iImageWidth;
pvi->bmiHeader.biHeight = m_iImageHeight;
pvi->bmiHeader.biPlanes = 1;
pvi->bmiHeader.biSizeImage = GetBitmapSize(&pvi->bmiHeader);
pvi->bmiHeader.biClrImportant = 0;
SetRectEmpty(&(pvi->rcSource)); // we want the whole image area rendered.
SetRectEmpty(&(pvi->rcTarget)); // no particular destination rectangle
pmt->SetType(&MEDIATYPE_Video);
pmt->SetFormatType(&FORMAT_VideoInfo);
pmt->SetTemporalCompression(FALSE);
// Work out the GUID for the subtype from the header info.
const GUID SubTypeGUID = GetBitmapSubtype(&pvi->bmiHeader);
pmt->SetSubtype(&SubTypeGUID);
pmt->SetSampleSize(pvi->bmiHeader.biSizeImage);
return NOERROR;
}
3.如何在输出Pin连接时进行媒体类型的检查?如下代码
//4.当输出Pin连接成功后，需要协商Pin上以后传送数据使用的Sample的一些属性，比如Sample使用的内存的大小等。
// CheckMediaType
//
// We will accept 8, 16, 24 or 32 bit video formats, in any
// image size that gives room to bounce.
// Returns E_INVALIDARG if the mediatype is not acceptable
//
HRESULT RtpStream::CheckMediaType(const CMediaType *pMediaType)
{
CheckPointer(pMediaType, E_POINTER);
if ((*(pMediaType->Type()) != MEDIATYPE_Video) || // we only output video
!(pMediaType->IsFixedSize())) // in fixed size samples
{
return E_INVALIDARG;
}
// Check for the subtypes we support
const GUID *SubType = pMediaType->Subtype();
if (SubType == NULL)
return E_INVALIDARG;
if ((*SubType != MEDIASUBTYPE_RGB8)
&& (*SubType != MEDIASUBTYPE_RGB565)
&& (*SubType != MEDIASUBTYPE_RGB555)
&& (*SubType != MEDIASUBTYPE_RGB24)
&& (*SubType != MEDIASUBTYPE_RGB32))
{
return E_INVALIDARG;
}
// Get the format area of the media type
VIDEOINFO *pvi = (VIDEOINFO *)pMediaType->Format();
if (pvi == NULL)
return E_INVALIDARG;
// Check the image size. As my default ball is 10 pixels big
// look for at least a 20x20 image. This is an arbitary size constraint,
// but it avoids balls that are bigger than the picture...
if ((pvi->bmiHeader.biWidth < 20) || (abs(pvi->bmiHeader.biHeight) < 20))
{
return E_INVALIDARG;
}
// Check if the image width & height have changed
if (pvi->bmiHeader.biWidth != m_Ball->GetImageWidth() ||
abs(pvi->bmiHeader.biHeight) != m_Ball->GetImageHeight())
{
// If the image width/height is changed, fail CheckMediaType() to force
// the renderer to resize the image.
return E_INVALIDARG;
}
return S_OK; // This format is acceptable.
}
//5.如何响应质量控制时事件。需要在输出Pin上实现Notify函数
// DecideBufferSize
//
// This will always be called after the format has been sucessfully
// negotiated. So we have a look at m_mt to see what size image we agreed.
// Then we can ask for buffers of the correct size to contain them.
//
HRESULT RtpStream::DecideBufferSize(IMemAllocator *pAlloc,
ALLOCATOR_PROPERTIES *pProperties)
{
CheckPointer(pAlloc, E_POINTER);
CheckPointer(pProperties, E_POINTER);
CAutoLock cAutoLock(m_pFilter->pStateLock());
HRESULT hr = NOERROR;
VIDEOINFO *pvi = (VIDEOINFO *)m_mt.Format();
pProperties->cBuffers = 1;
pProperties->cbBuffer = pvi->bmiHeader.biSizeImage;
ASSERT(pProperties->cbBuffer);
// Ask the allocator to reserve us some sample memory, NOTE the function
// can succeed (that is return NOERROR) but still not have allocated the
// memory that we requested, so we must check we got whatever we wanted
ALLOCATOR_PROPERTIES Actual;
hr = pAlloc->SetProperties(pProperties, &Actual);
if (FAILED(hr))
{
return hr;
}
// Is this allocator unsuitable
if (Actual.cbBuffer < pProperties->cbBuffer)
{
return E_FAIL;
}
// Make sure that we have only 1 buffer (we erase the ball in the
// old buffer to save having to zero a 200k+ buffer every time
// we draw a frame)
ASSERT(Actual.cBuffers == 1);
return NOERROR;
}
STDMETHODIMP RtpStream::Notify(IBaseFilter * pSender, Quality q)
{
// Adjust the repeat rate.
if (q.Proportion <= 0)
{
m_iRepeatTime = 1000; // We don't go slower than 1 per second
}
else
{
m_iRepeatTime = m_iRepeatTime * 1000 / q.Proportion;
if (m_iRepeatTime > 1000)
{
m_iRepeatTime = 1000; // We don't go slower than 1 per second
}
else if (m_iRepeatTime<10)
{
m_iRepeatTime = 10; // We don't go faster than 100/sec
}
}
// skip forwards
if (q.Late > 0)
m_rtSampleTime += q.Late;
return NOERROR;
} // Notify
先到这里，想起来再补充。