Fixing ffmpeg mov ‘error reading header’ ‘cannot allocate memory’

So I recently created a video with Filmic Pro on my iPhone for a podcast. The app 💩 itself abruptly in the middle of recording, and the resulting video would crash Premiere when imported. Quicktime would play it but not export or trim it. ffmpeg gave me the following:

% ffmpeg -i 
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 11.0.3 (clang-1103.0.32.62)
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fdf99806a00] error reading header Cannot allocate memory

This seemed to be a pretty severe error within the header parsing, such that no amount of “ignore error” options would override the failure.

Obviously this would not do; I even debated using screen recorder to record the quicktime output, but thankfully I found a trick that recovered the video.

Basically I opened the OSX 10.15 preview screen, and it the trim button. This then allowed me to trim off a wee bit of the video and the resulting output had correct headers. Highlight the file in Finder, press space, and then hit the little trim button that looks like a sideways iPhone with two arrows:

Second button from the left there

Also note that the Yodot MOV repair utility _did not_ work.