Ok, I know what is the issue here. I actually forgot that this used to be a problem, it did also affect professional equipment as well, not just iPhones. MP4 container (aka MOV or Quicktime format) used to use only 32 bit table for chunk offsets, which means file sizes over 4GB is not addressable in the MP4 file format. Now in the spec a 64 bit table is available, massively increasing max size of an QuickTime file. I guess the update of the file format spec and implementation must have been around the age of the iPhone 4/5. But you will likely come across older equipment with the same file size limitation when playing back mp4/qt files, and they will flat out refuse the 64 bit variant. Some equipment use multiple files and merge them together in the background.