The Track Reference Box provides a reference from the containing track to
another track in the presentation. These references are typed. A 'hint'
reference links from the containing hint track to the media data that it
hints. A content description reference 'cdsc' links a descriptive or
metadata track to the content which it describes.

Exactly one Track Reference Box can be contained within the Track Box.

If this box is not present, the track is not referencing any other track in
any way. The reference array is sized to fill the reference type box.

@author Alexander Simm

The reference type shall be set to one of the following values:

• 'hint': the referenced track(s) contain the original media for this
  hint track.


• 'cdsc': this track describes the referenced track.


• 'hind': this track depends on the referenced hint track, i.e., it
  should only be used if the referenced hint track is used.

@return the reference type

The track IDs are integers that provide a reference from the containing
track to other tracks in the presentation. Track IDs are never re-used
and cannot be equal to zero.
return  the track IDs this box refers to