USB Movies

I have a 8TB HDD connected via USB to my LGTV and I can watch MKV files but I have 2 problems.
1) I can't modify the thumbnails to create a custom thumbnail
2) I can't make chapters work unless if I split the entire MKV file into multiple parts with each representing a new chapter but then it won't show the length of the movie, it will only show the length of that chapter. I want to be able to select on a single file and skip to chapters using the skip forward button.