DecideBufferSize values seem to be ignored - c++

Question

I had the problem that when using a webcam as a source , the input sample was bigger than the size of the buffer provided by the allocator as you can see in the ASSERT statement in this code.
HRESULT MCMyOutputPin::Deliver(IMediaSample* sample)
{
HRESULT hr = NO_ERROR;
myLogger->LogDebug("In Outputpin Deliver", L"D:\\TEMP\\yc.log");
if (sample->GetActualDataLength() > 0)
{
IMediaSample *outsample;
hr = m_pAllocator->GetBuffer(&outsample, NULL, NULL, NULL);
if (FAILED(hr))
{
return hr;
}
BYTE* sampleBuffer = NULL;
BYTE* newBuffer = NULL;
long ulDataLen = sample->GetSize();
long datalenout = outsample->GetSize(); //this is always 92160
outsample->GetPointer(&newBuffer);
ASSERT(datalenout >= ulDataLen); //This fails
memcpy((void *)newBuffer, (void *)sampleBuffer, ulDataLen);
m_pInputPin->Receive(outsample);
outsample->Release();
sample->Release();
}
return hr;
//Forward to filter
}
So memcpy would definitely fails because you can't copy something into a buffer that is smaller than the data.
So I tried adjusting the buffersize in DecideBufferSize:
HRESULT MCMyOutputPin::DecideBufferSize(IMemAllocator *pAlloc, ALLOCATOR_PROPERTIES *pProps)
{
myLogger->LogDebug("On DecideBufferSIze", L"D:\\TEMP\\yc.log");
ALLOCATOR_PROPERTIES act;
HRESULT hr;
// by default we do something like this...
pProps->cbAlign = 1;
pProps->cBuffers = 30;
long buffersize = this->CurrentMediaType().lSampleSize * 3;
pProps->cbBuffer = 10 * 10 * 1000;
pProps->cbPrefix = 0;
hr = pAlloc->SetProperties(pProps, &act);
if (FAILED(hr)) return hr;
// make sure the allocator is OK with it.
if ((pProps->cBuffers > act.cBuffers) ||
(pProps->cbBuffer > act.cbBuffer) ||
(pProps->cbAlign > act.cbAlign))
return E_FAIL;
return NOERROR;
}
which gets ignored. The size of the sample returned by the alocator is always 92160.
I also made sure that the DecideBufferSize method gets actually called.
How do I set the size of the Buffer returned by Allocator->GetBuffer()?

Answer 1

MSDN states it pretty accurately:
Typically, the derived class will honor the input pin's buffer requirements, but it is not required to.
Buffer size decision is a matter of negotiation. Your setting requirements does not mean they will be accepted.
The size of the sample returned by the allocator is always 92160.
How do I set the size of the Buffer returned by Allocator->GetBuffer()?
What is wrong exactly with 92160, what makes you think it's invalid? You are looking for an answer to the wrong question. If you own allocator, then you set its buffer size. If you don't own and manage it, then you have to live with the size it already has.
I gave you MSDN link a few question ago, and it explains why increased size buffers are sometimes valid, and even more so - they are inevitable.