Q: QuickTime Player does not read sub file.

QuickTime Player 10.x: View movie subtitles

FWIW. it's been about 10 years since I tried to play a video in QuickTime Player with .srt files so I forgot abut the pitfalls. I also only have one video left as it turned out to test. The best solution is to use VLC.

You can let Apple know your view here…

http://www.apple.com/feedback/

What format is your Subtitle? I heard that SRT subtitles aren't compatible with QuickTime videos, you can should change SRT files to QT format, which is how QuickTime accepts caption or subtitle files. If you can't install another video player such as VLC, you also can try to hard burn subtitle to video with Pavtube Video Converter Ultimate, then your QuickTime doesn't need to read the video file and subtitle simultaneously.