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                                                   768
      CHAPTER 9                                                               Multimedia Features



      The following rules apply to these offsets:

      • For media types where an offset makes no sense (such as JPEG images), B and E
        are ignored, with no effect on viability.
      • When B or E are specified by time or frames, their value is considered to be rel-
        ative to the start of the next-level media clip. However, if E specifies an offset
        beyond the end of the next-level media clip, the end value is used instead, and
        there is no effect on viability.
      • When B or E are specified by markers, there is a corresponding absolute offset
        into the underlying media clip data object. If this offset is not within the range
        defined by the next-level media clip (if any), or if the marker is not present in
        the underlying media clip, the existence of the entry is ignored, and there is no
        effect on viability.
      • If the absolute offset derived from the values of all B entries in a media clip sec-
        tion chain is greater than or equal to the absolute offset derived from the values
        of all E entries, an empty range is defined. An empty range is legal.
      • Any B or E entry in a media clip section’s MH dictionary must be honored at
        play-time in order for the media clip section to be considered viable. (The entry
        might not be honored if its value was not viable or if the player did not support
        its value; for example, the player did not support markers.)
      • If a B or E entry is in a media clip section’s MH dictionary, all B or E entries, re-
        spectively, at deeper levels (closer to the media clip data), are evaluated as if
        they were in an MH dictionary (even if they are actually within BE dictionaries).
      • If B or E entry in a BE dictionary cannot be supported, it may be ignored at
        play-time.

                      TABLE 9.13 Entries in a media clip section MH/BE dictionary
KEY      TYPE            VALUE

B        dictionary      (Optional) A media offset dictionary (see “Media Offset Dictionary” on page 775)
                         that specifies the offset into the next-level media object at which the media clip sec-
                         tion begins. Default: the start of the next-level media object.

E        dictionary      (Optional) A media offset dictionary (see “Media Offset Dictionary” on page 775)
                         that specifies the offset into the next-level media object at which the media clip sec-
                         tion ends. Default: the end of the next-level media object.

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