Twice a week this month, Digiday will examine ways of “Improving Web Video.” We’ll cover both challenges and opportunities in online video and highlight brands and publishers getting it right. The series is made possible through the sponsorship of Vizu. The Web video market is large and growing fast. It is one of the few areas on the Internet that mostly has reversed the supply-demand imbalance that’s the hallmark of display advertising. In fact, online video publishers boast sell-through rates of 70 percent versus around 30 percent for display. That’s given sellers of online video more of an uppper hand, as demand for high-quality video placements outstrips supply. It’s also created a market where there’s pressure to fulfill…