I can see my video on the mini flip video when I play it back but when I play it on my Mac, I have a black screen and can only hear the audio.

I am using a mino flip camera. I can see the video on the camera but when I put it on mydesktop Intel imac I can only hear it. The screen is black. I downloaded the free Telestream software. I have two videos and on one, I can hear it but not see it and the other I keep getting a message saying "the doc could not be opened. A required codec is not available." What do I do now?