This is the resolution tag.
$ binwalk -e FHD-ARCHIVE-MIDV-908.mp4
DECIMAL HEXADECIMAL DESCRIPTION
0 0x0 MPEG-4 video file, version 0
Result: No hidden files or appended data were discovered after the moov atom. Extraction folder _<filename>.extracted is empty. FHD-ARCHIVE-MIDV-908.mp4
$ file FHD-ARCHIVE-MIDV-908.mp4
FHD-ARCHIVE-MIDV-908.mp4: ISO Media, MP4 Base Media v1 [ISO 14496-12] (avc1 / mp4a)
Interpretation: The file conforms to the ISO Base Media File Format (ISOBMFF) and contains at least one AVC (H.264) video track and an AAC audio track. This is the resolution tag
This is the most distinctive identifier. In media archiving, “MIDV” typically refers to a Series ID or Production Code. Result : No hidden files or appended data