Here's a file that is supposed to be exactly 0.5s long.

It has been produced by taking a wav file that's 0.5s long exactly and running this on a mac:

afconvert -s 3 -f mp4f -d aac half-a-second-44110-1ch.wav

It's got an elst saying the file has a start time of 2112 (typical for macOS AAC encoder), and a segment duration of 22050 (which is correct).

mp4parse-rust reports a duration of 24576, because it uses the duration of the track. mp4parse_get_fragment_info doesn't work because it doesn't look into the right box.