Apple’s QuickTime movie player used to be the bees’ knees in the video player world. It could do things other players couldn’t, like perfect forward and backwards frame-by-frame scrolling. It worked well, the user interface was simple. It was useful for obscure, niche things like inserting bookmarks and chapters into a video that didn’t have them, and was one of the few players which could play back high-definition videos fairly well. Today, having QuickTime on your computer is a security risk. If you’re still using it in some capacity and can’t find a replacement for it, consider disabling any permissions it has inside Windows Firewall. If you’re using a Mac, you can safely continue to use QuickTime without fear.
It emerged this past week that there are critical vulnerabilities present in the most recent version of QuickTime on Windows, and Apple has taken the executive decision to abandon the platform and stop supporting it. Apple’s reason is that most video on the internet is moving to HTML5 anyway, and no-one should ever need to use QuickTime ever again for streaming media. If you’re still using it for watching content encoded with the .mov container, consider using Handbrake to convert that media to .mp4 H.265 instead, or replace QuickTime with Media Player Home Cinema.