MyCloud 3TB - stored .MP4 video files recognized as music files in Samsung Smart TV

Couple of suggestions. Use a metadata editor like Mp3Tag to remove or change any of the metadata the mp4 video file my contain. Use a program like Handbrake to reencode the video using a different MP4 codec encoder. As indicated above you could have an encoding issue. A few times when the My Cloud Twonky DLNA server incorrectly categorizes a MP4 video as an audio file, reencoding the video using Handbrake typically solves the problem (for me).