If there weren't enough reasons to dislike Microsoft and W8.x, MS has apparently introduced problems with H264 MP4 video and the release of 8.1
I loaded GoPro studio2 only to find the MP4 export doesn't work, some investigation reveals similar problems with other video packages including Sony Vegas. Users are reporting non funcional MP4 export after the 8.1 upgrade where the export worked prefectly with W8.