Hi and welcome to Advanced Installer forum.
Thank you for your interest in Advanced Installer.
In order to achieve what you want, you must go to the Search page from the Custom Behavior group page, and create a
search of type "Registry key exists". In the "Registry Key" text field write the registry path for the QuickTime key (i.e. HKLM\SOFTWARE\Apple Computer, Inc.\QuickTime). The search value will be stored by default in the "RESULT_PROPERTY", but you can rename it.
Then for the installation to stop if the registry value is not found you can go in the "Custom" tab from the the Launch Condition page, click on the [New] button and in the "Condition" text field from the newly appeared dialog write the property created by your search (i.e. RESULT_PROPERTY).
The
Set launch conditions article might help you in a better understanding of how to create a custom launch condition.
Best regards,
Eusebiu