If QuickTime Player does not come up you will need to download it from the App Store. This is usually not the case since QuickTime Player comes preinstalled on most Mac computers.
To make QuickTime Player your default media player right-click your MP4 file. Click Get Info and select QuickTime Player under Open With. Click Change All and Continue to set it as your default player.
If the file does not open with Windows Media Player, do the following: Right-click the file Select Open With Select Windows Media Player from the drop-down menu.
You should download VLC Media Player from Videolan. org.
On Windows, download the zip file and right click on it. Select extract here and open the folder it creates. Click the launcher inside the folder to start the installation wizard. Follow the on-screen instructions to finish setting it up. On macOS, download the dmg file and double-click it. After entering your password it will start installing. If you get a message about it being a third-party app press ok.
