Create a Stream

A data stream context must be created before the AV/C Streaming filter driver, Avcstrm.sys, can provide services. The context points to an opaque structure that contains the requested data format, data-stream state, and properties, similar to a stream extension. A data format structure and the direction of the data flow are its input parameters. If the stream can be created successfully, it will return a stream context. This context is cached by the subunit driver and is used for subsequent AV/C Streaming requests.

This is a synchronous operation. The operation first creates a stream request structure to open a stream. It then calls the user-defined IRP synchronous routine to call the lower driver to create a data stream that is based on the given data flow direction and data format that is defined in AVCSTRM_FORMAT_INFO. The following code sample shows how to open a data stream context.

#include <avcstrm.h>

INIT_AVCSTRM_HEADER(pAVCStrmReq, AVCSTRM_OPEN);
pAVCStrmReq->CommandData.OpenStruct.AVCFormatInfo =            &AVCStrmFormatInfoTable[pDevExt->VideoFormatIndex]; 
pAVCStrmReq->CommandData.OpenStruct.AVCStreamContext = NULL;
pAVCStrmReq->CommandData.OpenStruct.DataFlow         = DataFlow;

Status = 
    AVCStrmReqSubmitIrpSynch( 
        pDevExt->pBusDeviceObject,
        pStrmExt->pIrpReq,
        pAVCStrmReq
        );

if(STATUS_SUCCESS == Status) {
    // Save the context, which is used for a 
    // Subsequent call to the AVCStrm filter driver    
    pStrmExt->AVCStreamContext = 
        pAVCStrmReq->CommandData.OpenStruct.AVCStreamContext;
}