I am not offering a way how to install QuickTime Player but offering alternative ways to play your files. As far as I know, Apple never really offered a Linux version
Regarding Installing Restricted Formats
According to the community wiki, you can install the restricted formats package via
sudo apt-get install ubuntu-restricted-extras
or
sudo apt install ubuntu-restricted-extras
Regarding Alternative Players Being Able to Play Files
As @JonasCz already mentioned, VLC might be a good option. You can install it via
sudo apt install vlc
In addition, there are smplayer and mplayer which should both be able to play all your files
sudo apt install smplayer
or for mplayer
sudo apt install mplayer
sudo apt-get install vlc
.