I am using a "new" but ex display, GoPro 3+ Black, and any video I record in 4K or 2.7K is saved as an MP4 file, but will only play audio when run through Windows Media Player, and the GoPro App refuses to do anything with the file it except say it is not in a compatible format. I am using a Sandisk Ultra 32GB class 10 SD card. What is the most likely problem - should I be using a different SD Card, or is there something else I am missing ? 1080p works fine. Thanks.