QuickTime 3 Reference
The Image Compression Manager supports hardware cursors introduced in PCI-based Macintosh computers, which eliminates cursor flicker. For all software codecs, this support requires no changes.
For codecs that manage the cursor themselves, QuickTime 2.1 provides a new flag, codecCompletionDontUnshield , for use when calling the ICMDecompressComplete ICMShieldSequenceCursor function. Use this flag to prevent the Image Compression Manager from unshielding the cursor when ICMDecompressComplete is called.