Audio plays but still no video after converting

I had to shoot some videos for a class. They recorded as MTS files so I converted them to MP4 using iSkysoft Video Converter.

When I opened them again in Final Cut Pro, I could only hear the audio and the viewer was black.

But if I open the converted footages on Quicktime, they work fine. The mp4's format is H.264, could it be the problem?