User-mode video capture drivers are responsible for notifying clients upon the completion of certain driver events. When a client sends a DVM_STREAM_INIT message, it indicates the type of notification, if any, it expects to receive. A client can specify any of the following notification targets:
User-mode drivers notify clients by calling the DriverCallback function in winmm.dll. This function delivers a message to the client’s notification target. The function also delivers message parameters, if the target type accepts parameters.
Video capture drivers must send MM_DRVM_OPEN, MM_DRVM_CLOSE, MM_DRVM_DATA, and MM_DRVM_ERROR messages to clients.
If you are using VCUser.lib to develop your driver, you do not have to call DriverCallback to send callback messages. Code within VCUser.lib handles delivery of callback messages for you, if you call VC_StreamInit when processing the DVM_STREAM_INIT message.