In its day QuickTime was bigger than Apple itself, so widely known that many who used it on their PCs weren’t even aware that it was an Apple product. As one of the first extensible frameworks for multimedia, from 1991 onwards it was at the forefront of computer audio and video. When the MPEG-4 format was standardised in 1998, it was based on QuickTime. For several years, sales of QuickTime-based products for Windows far exceeded those for Macs. Then, with the release of Catalina in October 2019, QuickTime was dead, leaving few Mac users now able to name its successor, AV Foundation (or AVFoundation, if you prefer), which had been introduced back in 2011.
For all intents and purposes, it died. Good riddance.