Media file format requires
        the 'iso2' brand in the compatible brands list since support of roll groups is required.
<a name="4.2"></a>
    4.2 Overview of Track Structure
        This clause summarizes requirements of the encapsulation of Opus coded bitstream as media data in audio tracks
        in file formats compliant with the ISO Base Media File Format. The details are described in clauses after this
        clause.
            + The handler_type field in the Handler Reference Box shall be set 