Date Fields and time zones in JPGs(ExifIFD, IFD0) and MP4s(Quicktime, Track1, 2)

[odog502]

Hi, I've perused this site, the forum, and the specifications to make sure I understand how all these date fields handle time and time zones.  Before I do a massive update to all my photos and videos, I wanted to run this by you folks to make sure I understand this all completely.  Let me know if any of my statements are incorrect.

1) MP4 time fields like the following are all assumed to be in UTC.  Some time zone agnostic equipment like non-GPS cameras store in local time only because they are not capable of determining time zone.

Code Select Expand

[QuickTime]     Create Date
[QuickTime]     Modify Date
[Track1]        Track Create Date
[Track1]        Track Modify Date
[Track1]        Media Create Date
[Track1]        Media Modify Date

2) "-api QuickTimeUTC" only affects the way these dates are extracted.  It doesn't impact how they are stored.  There is not a way to store time zone in these fields.

3) The following JPG fields are all assumed to be local time(i.e. the time at the location it was taken).

Code Select Expand

[IFD0]          Modify Date
[ExifIFD]       Date/Time Original
[ExifIFD]       Create Date         

4) There is not a way to add the time zone to the above IFD0 and ExifIFD date fields.  TimeZoneOffset is the only relevant field I found for storing time zone but it is apparently nonstandard and probably shouldn't be used.  ExifTool is intentionally designed to not write this field for this reason.

5) The date fields in the Quicktime, Track1, IFD0, and ExifIFD groups are still the most important date fields to use as they are the most ubiquitously utilized by other software(operating systems, DAMs, etc) for date sorting.

Here's all my sources for the above statements:
Quicktime group stored in UTC and "-api QuickTimeUTC":
https://exiftool.org/forum/index.php/topic,7241.msg36631.html#msg36631
https://exiftool.org/forum/index.php/topic,3416.0.html
Quicktime specification:
https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap1/qtff1.html
IFD0 and ExifIFD lack of time zone:
http://www.exif.org/Exif2-2.PDF
http://www.media.mit.edu/pia/Research/deepview/exif.html
http://www.exiftool.org/standards.html
https://exiftool.org/forum/index.php/topic,7326.msg37120.html#msg37120
TimeZoneOffset:
https://exiftool.org/forum/index.php/topic,6523.msg32557.html#msg32557

Thanks for the help.

[Phil Harvey]

You have a very good grasp of the situation.  I just have a couple of comments:

• The only way to store the time zone in EXIF using standard tags is by writing GPSTimeStamp.  Since GPSTimeStamp is in UTC and the other EXIF date/time tags are local, the time zone may be calculated.
• You haven't mentioned XMP at all.  Although not used yet by many DAM systems, it is slowly becoming more popular, and has the ability to store time zones.

- Phil

[odog502]

Thanks for reviewing my post and for the additional notes.  Those are helpful.  I will look into GPSTimeStamp.

Im just now starting to get into XMP.  In fact that was part of the massive update I was alluding too.  I just wanted to make sure that everything I had done so far was following best practices.

I've been approaching the photo metadata editing one step at a time.  After a few years of using ExifTool I finally completed the first and biggest phase which included universally applying a file naming convention, accurately dating photos and adding comments to photos(done with various perl scripts).  It took such a long time because many of my older photos(pre 2002) are paper scans and many post-2002 photos were taken with digital cameras before I cared much if the date settings were accurate!  Very tedious.  Now that they are all named by date, with accurate date/time stamps and comments, it will be much easier to make any future updates in batch.

My next step involves using more XMP and also attempting to use Daminion now that all my photos are normalized.  I was hoping to use Daminion for adding keywords and GPS data to photos(since it uses ExifTool on the back end) however I noticed a troubling bug where it strips the seconds off of Date/Time Original when the seconds are "00". Which is unfortunate because Daminion seemed to be one of the more robust DAMs for handling EXIF, XMP and IPTC.  As a sidenote to this, no originals are ever corrupted when I make changes or try something new.  I always verify with working copies before committing any changes to the originals.