Email harvesting means fetching email addresses by crawling web pages using various scripts/softwares. These email addresses then used for sending bulk marketing emails or newsletters/spams. There are lots of softwares/bots available in the market which crawls the website and gives email address from its pages. These softwares are generally known as "Harvesting Bot".
To have HTML5 Video on page is good and to have it with Closed Caption is even better, as it will make video accessible for physically challenged as well.