The issue is caused by the exe displaying the video not being signed. I downloaded a shareware AmCap from here http://noeld.com/programs.asp?cat=video
As installed, it works.
I used the Reshacker (resource editor) to remove the version information resource from amcap.exe which invalidated the signature. After that, it stopped working if AVAST is enabled and works if Avast is in Passive mode.
