That’s why sometimes you come across the error message like 'the movie could not be opened' or 'MP4 file not compatible with QuickTime' when trying to open MP4 files on Mac computer.

For instance, the default QuickTime Player plays MP4 videos encoded with MPEG-2, MPEG-4 or H.264 video codec and AAC audio codec only. In specific, MP4 is a container format which could include numerous different video audio codecs based on the usage, and also determines how an MP4 player can play an MP4 file on Mac most. If that happens, your app won't open the file or won't play back its audio or video' - from Apple

'Older or specialized media formats might not work in your app, because the format requires software designed to support it. So, if your QuickTime Player is outdated and lacks the right codecs to recognize certain MP4 videos, the MP4 files won't be played on Mac. Though MP4 is an Apple standard pushed with QuickTime 6 that by natural is playable on Mac with QuickTime player, QuickTime only plays MP4 files on Mac that have been encoded to meet Joint Video Team (JVT) standards. Free Download For Win 7 or later Table of Contents

Video players for mac quicktime vlc