HRESULT XAppCaptureReadLocalStream(
  XAppCaptureLocalStreamHandle handle,
  size_t startPosition,
  uint32_t bytesToRead,
  uint8_t * buffer,
  uint32_t * bytesWritten
)

const int MAX_DATA = 1024;

XAppCaptureLocalResult localResult = {0};
XAppCaptureLocalStreamHandle localHandle = nullptr;
HANDLE file = INVALID_HANDLE_VALUE;

uint8_t buffer[MAX_DATA];
/* 5 seconds, for example. You should call XAppCaptureGetVideoCaptureSettings() to ensure there's sufficient duration available */
uint64_t durationInMs = 5000;
size_t totalBytesRead = 0;
size_t fileSize = 0;

XAppCaptureRecordTimespan(nullptr, durationInMs, &localResult);

localHandle = localResult.clipHandle;
fileSize = localResult.fileSizeInBytes;

/* T:\ is one example of a writeable local directory. Be aware that the T:\ drive can be invalidated on suspend or resume, and as such it's better to use PLS */ 
file = CreateFileA("T:\\MyFile.mp4", GENERIC_READ | GENERIC_WRITE, 0, 0, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);

while (totalBytesRead < fileSize)
{
    uint32_t bytesRead = 0;
    uint32_t bytesWritten = 0;
    if (SUCCEEDED(XAppCaptureReadLocalStream(localHandle, totalBytesRead, sizeof(buffer), buffer, &bytesRead)))
    {
        WriteFile(file, buffer, bytesRead, &bytesWritten, NULL);

        totalBytesRead += bytesRead;
    }
    else
    {
        break;
    }
}

/* You must always close a local stream handle even if nothing was read in */
XAppCaptureCloseLocalStream(localHandle);