Track statistics always use "MOVIE" as TargetType
This is already a guess when creating a file with audio and video (it could be an episode or something else) and it is almost surely wrong when there is no video track. Probably best to just not write a TargetType (unless the other non-track-statistics-tags with TargetTypeValue 50 exist and have a consistent TargetType, but I don't know whether it is worth implementing this).