QuickTime File Format (Atoms & Flags)
They are a type of metadata specific to the QuickTime container.
They can contain all kinds of extra information for the video player to read out and use.


  QuickTime movie atoms have an atom type of 'moov'. These atoms act as
  a container for the information that describes a movie’s data. This
  information, or metadata, is stored in a number of different types of
  atoms. Generally speaking, only metadata is stored in a movie atom.
  Sample data for the movie, such as audio or video samples, are
  referenced in the movie atom, but are not contained in it.