Apple’s trusty QuickTime Player has been my go-to application for MP4-encoded video for the longest time; I actually bought QuickTime Pro because it was so handy.
And through 2018, it worked. Now I’m getting this abomination:
Dig far enough into Apple’s developer material, and you’ll find this:
QuickTime movie atoms have an atom type of ‘moov’. These atoms act as a container for the information that describes a movie’s data. This information, or metadata, is stored in a number of different types of atoms. Generally speaking, only metadata is stored in a movie atom. Sample data for the movie, such as audio or video samples, are referenced in the movie atom, but are not contained in it.
The movie atom is essentially a container of other atoms. These atoms, taken together, describe the contents of a movie. At the highest level, movie atoms typically contain track atoms, which in turn contain media atoms. At the lowest level are the leaf atoms, which contain non-atom data, usually in the form of a table or a set of data elements. For example, a track atom contains an edit atom, which in turn contains an edit list atom, a leaf atom which contains data in the form of an edit list table.
And so on, and so on, and scooby-dooby-doo. Scroll down some more, and you hit this:
Note: Profile atoms are deprecated in the QuickTime file format. The information that follows is intended to document existing content containing profile atoms and should not be used for new development.
So far as Apple is concerned, QuickTime for Windows is dead:
Important: QuickTime 7 for Windows is no longer supported by Apple. New versions of Windows since 2009 have included support for the key media formats, such as H.264 and AAC, that QuickTime 7 enabled. All current Windows web browsers support video without the need for browser plug-ins.
And this is one of a handful of MP4s that QuickTime will no longer play, presumably because the codecs have outgrown it:
I have other things I can play it on, but QT Pro was the most intuitive editor I had.