On input, MCI_BUFFER_PARMS should contain the number of buffers to be allocated, the size for each buffer, and a pointer to an array of MCI_MIX_BUFFER structures (one per buffer).

The mixer will attempt to allocate the number of buffers and size of buffers to use. If the mixer cannot satisfy the entire request, it will update the ulNumBuffers field with the total number of buffers that it was able to allocate. If no memory could be allocated, MCIERR_OUT_OF_MEMORY will be returned. If memory has already been allocated, and the MCI_ALLOCATE_BUFFER flag is used, MCIERR_INVALID_MODE is returned.