Note, this is for SMP v7.5.

 

While shooting your animation:

As a guide, go to the Settings > Advanced Settings menu item.

Select the button : Overlay

Choose from the TV Save zone panel, a 4:3 aspect ratio option, or 16:9 if you wish.

Click OK.

go to the View Menu

select Mask to Safe Zone aspect ratio

This will blank out the non 4:3 or 16:9 areas.

 

To export:

Now, when you export your movie, File  >  Make Movie

go to the Size panel   From the top drop down menu, choose:

Use TV Safe Aspect Ratio

and, from the bottom one:

Crop to size.