Changing Time Zone for Video

[SSherris]

I'm trying to edit time stamps for videos so uploads to Google Photos sort correctly.  (Photos use DateTimeOriginal which is easy)

1) -CreateDate does not have a time zone in the data (format is yyyy:mm:dd hh:mm:ss)
2) -ModifyDate does not have a time zone in the data
3) -system:FileModifyDate *does* have a time zone, but I can't change it!
       For example, if the original time shows as "2016:08:30 16:56:27-04:00" but I try to change it to "2016:08:30 16:56:27-00:00", I end up with "2016:08:30 12:56:27-04:00" instead.  Yes, that's technically the same moment in time, but it's not right
4) -timezone data is empty, and replacing it with +00:00 seems to do nothing

If -timezone isn't a valid tag, why does exiftool insist on keeping the video file in the -4 TZ?  How do I fix this?

Thanks!

[Phil Harvey]

3) -system:FileModifyDate *does* have a time zone, but I can't change it!
       For example, if the original time shows as "2016:08:30 16:56:27-04:00" but I try to change it to "2016:08:30 16:56:27-00:00", I end up with "2016:08:30 12:56:27-04:00" instead.  Yes, that's technically the same moment in time, but it's not right

The System date/time tags use the system time zone.  You can only change this with your system settings.

In theory, QuickTime timestamps should be UTC, but many cameras don't follow this rule so by default ExifTool doesn't try to apply a time zone to these.

- Phil