from windows_common.h:301
struct winusb_transfer_priv
{
uint8_t interface_number;
uint8_t *hid_buffer;
uint8_t *hid_dest;
size_t hid_expected_size;
void *iso_context;
void *isoch_buffer_handle;
BOOL iso_break_stream;
libusb_transfer_cb_fn iso_user_callback;
};