convey initializing information for the decoder.
                See 4.3.2 Opus Specific Box to get the details.
            + An Opus sample is exactly one Opus packet for each of different Opus bitstreams.
                See 4.3.3 Sample format to get the details.
            + Every Opus sample is a sync sample but requires pre-roll for every random access to get correct output.
                See 4.3.6 Random Access to get the details.
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    4.3 Definitions of Opus sample
        4.3.