Preview and Overlay Modes

A capture driver can implement two methods for viewing an incoming video stream: preview mode and overlay mode. If a capture driver implements both methods, the user can choose which method to use.

Preview mode transfers digitized frames from the capture hardware to system memory and then displays the digitized frames in the capture window by using graphics device interface (GDI) functions. Applications might decrease the preview rate when the parent window loses focus, and increase the preview rate when the parent window gains focus. This action improves general system responsiveness because the preview operation is processor intensive.

There are three messages to control the preview operation.

When preview and scaling are both enabled, the captured video frame is stretched to the dimensions of the capture window. Enabling preview mode automatically disables overlay mode.

Overlay mode is a hardware function that displays the contents of the capture buffer on the monitor without using CPU resources. You can enable and disable overlay mode by sending the WM_CAP_SET_OVERLAY message (or the capOverlay macro) to a capture window. Enabling overlay mode automatically disables preview mode.

You can also set the scroll position of the video frame within the client area of the capture window for preview mode or overlay mode by sending the WM_CAP_SET_SCROLL message (or the capSetScrollPos macro) to a capture window.

Software for developers
Delphi Components
.Net Components
Software for Android Developers
More information resources
Unix Manual Pages
Delphi Examples
Databases for Amazon shops developers
Amazon Categories Database
Browse Nodes Database