"TV" would be the setting in this study if we concerned with media effects. The setting is the environment in which the study is carried out so, since this is a media study investigating TV ads, that would be the setting. You might have called this a constant since all the participants watched a TV ad and that would be a true statement but it is not as precise as we are trying for in our thinking. It would be like the police asked you, "How did the robber escape?" and you said, "He left in a vehicle."
If we were analyzing this in a methods course another setting identified could be a mall since that is the location where the study was carried out. That is an overly concrete point for our purposes and, given the information you had, we could most precisely say, " TV was the setting and it was a constant since no other media, e.g. magazines, radio, internet,... were included in the study."