Filter Settings and Rebuild Graph
The filters option lists the active DirectShow components. Selecting one of them opens its property page window. Usually it is not necessary to apply any changes there, and you should only try to adjust these settings if you know what you are doing. This doesn't work with the NVIDIA decoder, there you have to use its tray icon.
The command rebuild graph resets all DirectShow filters and starts them again. In this way possible problems with distorted audio or video can be solved. Such problems can occur when using the fast channel switching (see Settings/DirectX). This may happen with certain audio decoders, when switching to another channel with a lower audio bit-rate (e.g. from stereo to mono), resulting in a sound, that is periodically interrupted and played to fast (sounds like Mickey Mouse voices).
Rebuilding the graph is also needed for certain changes you have applied in the options window to take effect (for example selecting another video decoder in combination with Marfi's or the DVBViewer source filter).
Additional information about DirectShow filters can be found in chapter 10.