 key needed to decrypt it.
        This association is signaled either through the specification of a
        default key ID in the track encryption box ('tenc') or by assigning the
        sample to a Sample Group, the definition of which specifies a key ID.
        Streams may contain a mixture of encrypted and unencrypted samples.
      </p>
    </section>

    <section id="detect-format">
      <h2>Detection</h2>
      <p>
        For a stream determined to be in the ISO Base Media File Format
        [