This video shows replication of individual pieces of double stranded DNA. This is the first time DNA replication -- arguably, the fundamental process of life on Earth -- has been observed directly.
Each glowing strand is a piece of double helix growing by replication at the left-hand end. They move at different speeds and stop and start. Dark gaps in the line are single-stranded DNA where one polymerase failed to attach (the fluorescent dye only binds double-stranded DNA).
Some surprises come out of being able to observe replication directly. For example, the two polymerases involved in replication (one for each strand) aren't coordinated. They stop and start at random, but overall they move at the same average speed, so everything works out. This stochastic model is quite different from a smooth-running, coordinated machine usually imagined.