Question about a certain effect...

[Arigatomina]

If you want to make it simple, there's no need for anything. Just take your clip, apply the 'fade out to white' and cut the last 3 'frames' of it. The white flash will be tiny and quick. Just make sure to undo the effect on the rest of the clip so the fade only happens on the very short section.

One benefit of using a matte instead is that it isn't pure white, not so hard on the eyes. Using a white picture (or even a white part of the video) and fading in and out to it gives you a sharp, pure white flash. Do that a lot and chances are you'll get the usual complaints.