Following an older post: http://www.zenphoto.org/support/topic.php?id=11768
I tried to add metadata fields with only partial success.

From exiftool tag names ( source: http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/QuickTime.html), I found:
"©cmt" Comment

While running exiftool, I got the following two results:
exiftool json output
"Comment": {
"desc": "Comment",
"id": "?cmt",
"val": "Comments go here"

exiftool -G output
[QuickTime] Comment : Comments go here

Using that information, I added (some whitespace removed here):
'VideoComment' => array('QuickTime', 'Comment', gettext('Video Comment'), false, 256, true, 'string'),
after the other Video tags, in the functions.php file.

Going into options, "Video Comment" appears in the metadata list, but enabling it doesn't produce any display. I tried with both GD and Imagick, and refreshed the metadata, but they never show with the other Video metadata.

Config info:
ZP 1.4.10 [3d5be820ca]
PHP Imagick library 3.1.0RC1
ImageMagick 6.6.9-7 2014-03-06 Q16
MySQLi version: 5.5.44
PHP version: 5.3.10-1ubuntu3.20
Current gallery theme: Libratus

Thanks for any advice

P.S. I'm getting messages that my functions.php file seems wrong, although everything is working except for my new metadata.