The obscure technical question thread

[Deech]

Question: When a piston crosses top dead centre and starts to reverse its directon, for an instant its velocity has to equal zero. (Can't change direction without stopping)

So does that mean the entire rotating assembly of an engine stops completely twice per revolution (on a flat-plane crankshaft), or do the connecting rods stretch; letting the crankshaft keep rotating, but for the pistons come to a halt?

It's just something that's got me stumped
Thanks in advance