If you are unable to open an MP4 file on our media player, try changing the video format. There are many good video converters available on the internet that can help you convert your MP4 to MP3, AVI, ...

For example, if you want that all your MP4 files are opened in VLC media player by default, you will have to right click on the file, click “Open As” and choose an app from the list as well as check ...