The baby will speak whatever languages it encounters the most. Not just the languages the parents speak, but also the languages spoken by other children/people in the baby's daily life as well as on programs, music, etc that the baby watches/hears.
There are cases where the baby might speak both, and other ones where he/she will only be competent in one of those languages. Plus, it's entirely possible the baby will speak neither language, if the parents live in a community dominated by a third language.
Generally speaking, if there is only one person who speaks a language to the baby on a regular basis, and many people who speak the other language regularly, the child becomes competent only in the one spoken by the majority. He/she may passively understand the minority language, but often will not speak it himself/herself. Of course, there are exceptions.