Sorry, went on vacation and forgot about this post earlier. I mean the actual rotation tag within a video. Such as if you record a video with your phone and it sees your orientation as vertical it will set a rotation tag within the metadata. Playing a high res mp4 video will play the audio and a messed up video image within the player. I found if I strip or set the rotation to 0 it will work again in heresphere. A link explaining the tag might be better so will link below.
I can reproduce the problem by taking any I think 4k video, although just noticed I use 5k, don't think matters and using exiftool or ffmpeg and add rotation to 90. Link below to explain usage. You could also take a high res vertical video on your cell and think it should cause the problem if it recognizes the rotation correction.
You can also use exiftool to see the metadata tags if needing to know if set to 90.
https://superuser.com/questions/1307158/change-rotation-flag-in-mp4-video-withou...