Belt does not move. Sound is not coming from that area of engine. Its over the two cylinders closest to drivers side. Not as rhythmic as the sound in the video.

Hmm..Well the TC is on that side.Does it sound similar to the video kind of a light hollow knock or a deep knock?

Here is a link to the sound my car is making. This is not my vehicle but, it sounds exactly the same.
http://youtu.be/P2AQjAx7ZXk

If that'* what it sounds like, then it sure sounds like a spun rod bearing.

Best to just replace the motor?

You have 2 options. Replace the motor, or replace the short block. If you have the tools, you can pick up a good short block way cheaper then a full long block. And then transfer all your parts over. Perhaps $200 in gaskets and bolts. Head gaskets, head bolts, harmonic balancer bolt unless the HB is still on the short block. And your intake manifold gaskets.

Dude your engine has just died. How did you get that 3800 to make a noise like that? If you starved it for oil it may be a consequence of negligence. There'* this one guy on YouTube that had knock on his 1990 Buick LeSabre. To get such a reliable engine to do that is incredible. Like the others said replace your engine.