为什么WMVIDEOINFOHEADER.rcSource导致无效指针

Question

我不明白这一点：((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->rcSource = rc;导致（WM_MEDIA_TYPE *）VideoMediaType成为invaid。当代码块的其余部分似乎没有问题时。

WM_MEDIA_TYPE* VideoMediaType = NULL;
VideoMediaType = (WM_MEDIA_TYPE*) new BYTE[MediaType];

Status = VideoMediaProps->GetMediaType(VideoMediaType, &MediaType);
RECT rc;
rc.left   = 0;
rc.top    = 0;
rc.right  = 640;
rc.bottom = 480;

((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->rcSource = rc; //<--Causing the issue.
((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->rcTarget = rc;
((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->dwBitRate = BitRate;
((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->AvgTimePerFrame = ( (LONGLONG) 10000000 ) / ( (LONGLONG) 30 );
((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->bmiHeader.biHeight = GetSystemMetrics(SM_CYSCREEN);
((WMVIDEOINFOHEADER*)&VideoMediaType->pbFormat)->bmiHeader.biWidth  = GetSystemMetrics(SM_CXSCREEN);

无论我把这行放在哪里，一旦调试器在调试模式下进入该行，VideoMediaType＆＃39;变得无效。如果我注释掉该行，则指针保持有效并且程序按预期执行。