The default autofocus mode in both live view and movie modes is Face Detect and Tracking. Using the 18-135mm STM kit lens, the Canon EOS 70D managed to track our subject, but did so in steps, not quite as evenly as we'd have hoped. If you look at the deck work behind the subject, you can see it doesn't start to move out of focus until about the four-second mark, then it moves stepwise as she continues forward. It also doesn't look like it needs to focus until the four-second mark, so bear that in mind.