Problems with opening a video file with a common video player

It is widely known the huge number of different video formats that exists nowadays: mp4, mkv, avi, dvd, wmv, mov... This variety of formats allows us to choose whether we need more quality or maybe we need a video which occupies less memory in our computer. However, this represents drawbacks as well. The most known and important is the impossibility of playing a certain video in a common video player such as Windows Media, just because the camera with which it has been recorded, records the videos with a certain format.