If you need QuickTime for Pro editing or legacy exporting, the 7.5.5 DMG is safe to use if obtained from Apple’s official archive links above.
Try this direct link to Apple’s servers (copy and paste into your browser): quicktime 7.5.5 download for mac 10.5.8
https://support.apple.com/downloads/DL923/en_US/QuickTime755.dmg If you need QuickTime for Pro editing or