Looks like if a non standard tag is added by, for example, ffmpeg, AtomicParsley reports on all of the tokes, but called them the empty string. If the example below I've removed the extraneous ffprobe output:
$ AtomicParsley file.mp4 -t
Atom "©nam" contains: Title
Atom "©too" contains: Lavf58.20.100
Atom "©cmt" contains: Comment
Atom "©day" contains: 2023
Atom "desc" contains: Description
$ ffprobe -i file.mp4 -print_format json -show_format
< deleted >
"format": {
"filename": "file.mp4",
"nb_streams": 2,
"nb_programs": 0,
"format_name": "mov,mp4,m4a,3gp,3g2,mj2",
"format_long_name": "QuickTime / MOV",
"start_time": "0.000000",
"duration": "2100.235000",
"size": "362797503",
"bit_rate": "1381931",
"probe_score": 100,
"tags": {
"major_brand": "isom",
"minor_version": "512",
"compatible_brands": "isomiso2avc1mp41",
"creation_time": "2023-04-03T03:06:47.000000Z",
"title": "Title",
"encoder": "Lavf58.20.100",
"comment": "Comment",
"date": "2023",
"description": "Description"
}
}
$ ffmpeg -i file.mp4 -movflags use_metadata_tags -metadata newTag="newTag" -c copy file2.mp4 >/dev/null 2>&1
$ AtomicParsley file2.mp4 -t
Atom "" contains: isom
Atom "" contains: 512
Atom "" contains: isomiso2avc1mp41
Atom "" contains: Description
Atom "" contains: Title
Atom "" contains: newTag
Atom "" contains: Comment
Atom "" contains: 2023
Atom "" contains: Lavf59.27.100
$ ffprobe -i file2.mp4 -print_format json -show_format
< deleted >
"format": {
"filename": "file2.mp4",
"nb_streams": 2,
"nb_programs": 0,
"format_name": "mov,mp4,m4a,3gp,3g2,mj2",
"format_long_name": "QuickTime / MOV",
"start_time": "0.000000",
"duration": "2100.199000",
"size": "362797671",
"bit_rate": "1381955",
"probe_score": 100,
"tags": {
"minor_version": "512",
"major_brand": "isom",
"compatible_brands": "isomiso2avc1mp41",
"description": "Description",
"title": "Title",
"newTag": "newTag",
"comment": "Comment",
"date": "2023",
"encoder": "Lavf59.27.100"
}
}