This issue has cropped up on some High Sierra installations that have never had Replay Video Capture installed before. Here's the workaround:

Download Soundflower High Sierra

Run the Replay Video Capture installer again and perform an install
When the installer tells you that the installation failed, go to System Preferences > Security & Privacy > General. Then click on “Allow” next to “Replay Video Capture”
Re-run the Replay Video Capture installer again and finish the installation

Download Soundflower For Windows

If you do not see Replay Video Capture in the System Preferences > Security & Privacy > General immediately after a failed install then please install Soundflower directly from this page:

Alternative To Soundflower

Who Made Soundflower

Our software library provides a free download of Soundflower 2.0 for Mac. Our antivirus analysis shows that this Mac download is safe. Commonly, this program's installer has the following filename: Soundflower-1.5.2.dmg. The following versions: 1.6 and 1.5 are the most frequently downloaded ones by the program users. Soundflower is an application that creates a virtual audio channel and directs audio input and output to physical or virtual devices. Audacity is a free application for recording and editing sounds. TextEdit is the default text editor/word processor that is included in Mac OS X. The macOS High Sierra 10.13.2 update improves the stability, compatibility and security of your Mac, and is recommended for all users. This update:. Improves compatibility with certain third-party USB audio devices. Improves VoiceOver navigation when viewing PDF documents in Preview. Improves compatibility of Braille displays with Mail. Soundflower installation fails on High Sierra Modified on: Wed, 14 Feb, 2018 at 7:15 PM This issue has cropped up on some High Sierra installations that have never had Replay Video Capture installed before.