[Jason Cahapay]

Encountered the same issue, it’s weird you can’t install it when your system meets the minimum requirements.

Here’s a workaround,

1. Mount the Decklink_Macintosh_7.2.6.dmg
2. Copy the contents to your desktop.
3. Control+click Decklink Installer 7.2.6 and Show Package Contents.
4. Control+click distribution.plist and open with TextEdit.
5. Edit the ff.

my.target.systemVersion.ProductVersion >= ‘10.6’ to my.target.systemVersion.ProductVersion >= ‘10.5’

system.version.ProductVersion >= ‘10.6’ to system.version.ProductVersion >= ‘10.5’

6. Save and install.

Got it working and testing it right now, seems to working fine but I would still advice you to try it at your own risk. =)