DVM_STREAM_PREPAREHEADER

Notifies a video capture driver to prepare an input buffer for video streaming.

Returns DV_ERR_OK if successful or an error code otherwise. The following errors are defined:

DV_ERR_NOMEM	Indicates the driver is unable to allocate or lock memory.
DV_ERR_NOTSUPPORTED	Unable to prepare data block. (This return lets MSVIDEO prepare the data block.)

dwParam1: Address of a VIDEOHDR structure identifying the buffer.
dwParam2: Size, in bytes, of the VIDEOHDR structure.

The VIDEOHDR data structure and the data block pointed to by its lpData field must be allocated with GlobalAlloc using the GMEM_MOVEABLE and GMEM_SHARE flags, and locked with GlobalLock. Preparing a header previously prepared will have no effect, and the message will return zero. Typically, this operation is used to ensure that the buffer will be available for use at interrupt time.