It may not be the best effect ever made, but it was cheap.

Get a nice piece of single strength glass and some sort of black background (REAL black).

Set the black background on the ground and light it so that no possible reflection off the material goes straight into the lens. There IS a reflection off many black materials. You can alpha off this.

Place the glass above the background on two supports. I used bricks. Light to avoid reflections. Look VERY carefully, you may not be seeing ordinary reflections that you are used to seeing. They sneak in.

Mount the camcorder at a respectable distance above the setup. There WILL be flying glass. Put something flat and thin on the glass and manually focus on it at extreme telephoto, then reset the zoom as needed. The edge of a sheet with writing on it is fine. Then remove the object. This will assure that the focus is on the area where the shatter occurs.

Get AND WEAR some good heavy gloves and a jacket and safety glasses.

Take a fair sized hammer and whack the glass near one of the edges near one of the supports. If you hit halfway between the supports, there is a good chance of an even straight split up the middle. If you hit off center, the result is more likely to be a shatter.

Make sure that the glass is big enough so that the edges and the hammer and supports are not videoed.

Be VERY careful. You didn't hear this here. But it works just fine. And this type of glass is VERY cheap. Get several pieces. 10 x 15" is plenty big enough. Bigger might be better, but the money might be a consideration. Even consider whacking two or three stacked. That makes a dramatic shatter.

But, be VERY careful. Do this at your OWN risk. Then clean up. Vaccuum if at all possible, as you will likely have a lot of very tiny fragments. There are children who play in my yard. I didn't want any injuries.

You might use VV to slow down the actual fracture.

The effect worked well.

You can also Chroma Key the whole thing if you have the proper background.