

Quit QuickTime Player using Activity Monitor and then restart.Convert video files to another format that can be supported by QuickTime.Change the extension of the video files which can’t be played.

Update QuickTime Player to the latest version.Please try these solutions when QuickTime Player can’t open your video files:

Possible causes include: incompatible or outdated QuickTime Player, the video file is corrupted somehow, and Mac system issues. What causes this issue and how to fix it? Some Mac users said they can’t play videos in QuickTime all of a sudden. How to Troubleshoot QuickTime Player Not Opening Videos You can use the playback controls which will appear when you place the pointer over the screen to play and control your file: it allows you to fast-forward play, reverse play, and change the playback speed.
