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    4.1 File Type Identification<a name="4.1"></a>
        This specification defines the brand 'Opus' to declare files are conformant to this specification. Additionally,
        files conformant to this specification shall contain at least one brand, which supports the requirements and the
        requirements described in this clause without contradiction, in the compatible brands list of the File Type Box.
        As an example, the minimal support of the encapsulation of Opus bitstreams in ISO Base 