What are they:

Blanking presets are files that can be created with WinDVD Tweaker to store certain Blanking configurations. Although the automatic calculation of blanking bars should be enough for most people this facility is here incase someone needs it. The files carry the file extension ".blk" and can only be loaded from within WinDVD Tweaker.

All blanking presets that are found in the WinDVD Tweaker folder, will be added to the list in the program so you can select whatever one you like from the drop down list.

Extension:

.blk