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                                                    771
          SECTION 9.1                                                                  Multimedia



          ration may be modified when a media clip section (see “Media Clip Section” on
          page 767) is used: the intrinsic duration is the difference between the absolute be-
          gin and end offsets. For a media type having no notion of time (such as a JPEG
          image), the duration is considered to be infinity.

          If the simple duration is longer than the intrinsic duration, the player should
          freeze the media in its final state until the simple duration has elapsed. For visual
          media types, the last appearance (frame) would be displayed. For aural media
          types, the media is logically frozen but should not continue to produce sound.

          Note: In this case, the RC entry, which specifies a repeat count, applies to the simple
          duration; therefore, the entire play-pause sequence is repeated RC times.

                            TABLE 9.16 Entries in a media duration dictionary
KEY     TYPE              VALUE

Type    name              (Optional) The type of PDF object that this dictionary describes; if present, must be
                          MediaDuration for a media duration dictionary.

S       name              (Required) The subtype of media duration dictionary. Valid values are:
                              I           The duration is the intrinsic duration of the associated media
                              F           The duration is infinity
                              T           The duration is specified by the T entry
                          The media duration dictionary is considered non-viable if the viewer application
                          does not recognize the value of this entry.

T       dictionary        (Required if the value of S is T; otherwise ignored) A timespan dictionary specifying
                          an explicit duration (see Table 9.24). A negative duration is illegal.


    9.1.5 Media Screen Parameters

          A media screen parameters dictionary (see Table 9.17) specifies where a media
          object should be played. It contains MH and BE dictionaries (see Table 9.18),
          which function as discussed in Section 9.1.1, “Viability.” All media clips that are
          being played are associated with a particular document and must be stopped
          when the document is closed.

          Note: It is recommended that viewer applications disallow floating windows and
          full-screen windows unless specifically allowed by the user. The reason is that docu-
          ment-based security attacks are possible if windows containing arbitrary media con-
          tent can be displayed without indicating to the user that the window is merely

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