windowscentral[.]com/software-apps/microsoft-defender-vs-vlc-which-is-causing-mp3s-to-take-30-seconds-to-load
Defender doesn't like VLC, at least currently. The discussion focuses on MP3s, though I wouldn't be surprised if other media formats weren't similarly effected. If you have problems the simplest fix is add the VLC folder to Defender's exceptions -- files in places it won't look at.