The Preview Resource(IM: QC)

Inside Macintosh: QuickTime Components /

Chapter 12 - Preview Components / Preview Components Reference

The Preview Resource
QuickTime uses the preview resource (defined by the pnotResource data type) with
a resource ID of 0 to store the visual preview information. The structure of the preview resource is shown in Listing 12-3.

WARNING
If you parse this resource directly, please do extensive error checking in your code so as not to hinder future expansion of the data structure. In particular, if you encounter unknown version bits, exercise caution. Unexpected results may occur.
Listing 12-3 The preview resource
typedef struct pnotResource {
   unsigned long  modDate;    /* modification date */
   short          version;    /* version number of preview
                                 resource */
   OSType         resType;    /* type of resource used as preview
                                 cache */
   short          resID;      /* resource identification number
                                 of resource used as preview
                                 cache */
   short          numResItems;/* number of additional file
                                 descriptions */
   pnotResItem    resItem[ ]; /* array of file descriptions */
} pnotResource;
Field Description

modDate
Contains the modification time (in standard Macintosh seconds since midnight, January 1, 1904) of the file for which the preview was created. This parameter allows you to find out if the preview is out of date with the contents of the file.
version
Contains the version number of the preview resource. The low bit
of the version is a flag for preview components that only reference their data. If the bit is set, it indicates that the resource identified in the preview resource is not owned by the preview component,
but is part of the file. It is not removed when the preview is
updated or removed (using the Image Compression Manager's MakeFilePreview or AddFilePreview function), as it would be if the version number were 0.
resType
Contains the type of a resource used as a preview cache for the given file. The type of the resource determines the subtype of the preview component that should be used to display the preview.
resID
Contains the identification number of a resource used as a preview cache for the specified file.
numResItems
Specifies the number of additional file descriptions stored with this preview.
resItem
Contains the preview resource item structure (defined by the pnotResItem data type), which is described next.