Rename MP4 files based on shifted date/time but retaining original date tags

[John Derbyshire]

Hi all, I'm trying to rename a folder full of MP4 files to reflect FileModifyDate but with the date/time shifted back 6 hours to reflect the different time zone at the time the footage was taken.

I know I can use the following to set the filenames based on the current value of FileModifyDate:

   exiftool '-FileName<FileModifyDate' -d '%y%m%d %H%M%S%%-c.%%e' .
   
But how do I shift the time, ideally without overwriting the current value of FileModifyDate (so that the rename process is repeatable)?

[StarGeek]

You could use the GlobalTimeShift option
exiftool '-FileName<FileModifyDate' -globalTimeShift -6 -d '%y%m%d %H%M%S%%-c.%%e' .

or the ShiftTime helper function
exiftool '-FileName<${FileModifyDate;ShiftTime("-6")}' -d '%y%m%d %H%M%S%%-c.%%e' .

Note that, as the name says, the -globalTimeShift affects all date/time tags, so you don't want to use it if you are doing other operations at the same time.

[John Derbyshire]

Firstly, many thanks StarGeek for taking the time to provide the two suggestions.

The first option works fine, and by following your link to the globalTimeShift option I was then able to find https://exiftool.org/Shift.html, from which I could see that I could make a more fine-grained shift (subtracting 6 hours, 1 minute and 47 seconds for example, which I realised I needed to do to bring my camera MP4 footage into line with network time from the photos from my phone camera). So this is what I am using for now:

   exiftool '-FileName<FileModifyDate' -globalTimeShift '-0:0:0 6:1:47' -d '%y%m%d %H%M%S%%-c.%%e' .
   
I have had less success with the second option though. It doesn't report any issues, but it looks like globalTimeShift is doing the work there too, because it doesn't matter what I put in as the ShiftTime value it just seems to do the "-6" from globalTimeShift. So the "-12" appears to be ignored in the following:

   exiftool '-FileName<${FileModifyDate;ShiftTime("-12")}' -globalTimeShift -6 -d '%y%m%d %H%M%S%%-c.%%e' .

I am using the Windows version by the way, in case that makes a difference.

The reason I'd like to persevere with the second option is that it looks similar to a solution that would also shift the timestamp in the filename to reflect the start date/time of the footage rather than the end date/time (by subtracting the clip duration). See https://exiftool.org/forum/index.php?topic=10683.0, although I have not been able to get this to work either.

Ideally I am looking for something that will (a) take the FileModifyDate and subtract e.g. 6h 1m 47s from that then (b) subtract the clip duration from that to give a filename that represents the start date/time of the clip.

My best attempt would be:

   exiftool "-filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'))}" -globalTimeShift '-0:0:0 6:1:47' -d '%y%m%d %H%M%S%%-c.%%e' .

But this results in the following:
   

Code Select Expand

exiftool : Warning: No writable tags set from ./240411 204312.MP4
At line:1 char:1
+ exiftool "-filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValu ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (Warning: No wri...0411 204312.MP4:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError
 
Warning: No writable tags set from ./240411 204442.MP4
    1 directories scanned
    0 image files updated
    2 image files unchanged

Would be very grateful for any further suggestions.

[StarGeek]

I have had less success with the second option though.

That's because I made a copy/paste error.  It's supposed to be either -globalTimeShift or ShiftTime, not both.  I've corrected my post.

I am using the Windows version by the way, in case that makes a difference.

It does.  I had assumed by your quotes that you were on Mac/Linux. But you appear to be using Powershell. I can't give you the correct command, since I've given up trying to figure out PS's strange quoting rules. I can only suggest that you swap the double/single quotes and use CMD.

My best attempt would be:

    exiftool "-filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'))}" -globalTimeShift '-0:0:0 6:1:47' -d '%y%m%d %H%M%S%%-c.%%e' .

Try this in CMD, except change the single quotes into double quotes for this part of the command
-globalTimeShift "-0:0:0 6:1:47" -d "%y%m%d %H%M%S%%-c.%%e"

[John Derbyshire]

I am indeed using PowerShell, but will switch to CMD while I try to get this working.

When I run the following it does the globalTimeShift but it doesn't subtract the duration from the shifted time:

   exiftool "-filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'))}" -globalTimeShift "-0:0:0 6:1:47" -d "%y%m%d %H%M%S%%-c.%%e" .

When I remove the globalTimeShift and run the following, it sets the filename back to the original FileModifyDate but again does nothing with the duration:

   exiftool "-filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'))}" -d "%y%m%d %H%M%S%%-c.%%e" .

Stripping it back to your second suggestion, it runs without errors but also doesn't change anything:

   exiftool "-FileName<${FileModifyDate;ShiftTime('-6')}" -d "%y%m%d %H%M%S%%-c.%%e" .

So it feels like in all cases ShiftTime is not operating on the FileModifyDate for some reason.

Again, very grateful for any suggestions as to how to get this working.

[Phil Harvey]

The problem is that ShiftTime only works for standard-format date/time values, so it won't work with a value formatted arbitrarily using the -d option.

You may do what you want in separate steps, but it requires applying the shifts to some date/time value before copying them to the file name in the last step.  You can use a date/time tag in a sidecar file if you won't want to modify the originals.

- Phil

[StarGeek]

I think that's correct.  Changed from the -d (-dateFormat) option to the DateFmt helper function, changed the -globalTimeShift into another ShiftTime.

Code Select Expand

C:\>exiftool -G1 -a -s -FileModifyDate -Duration Y:\!temp\Test1.mp4
[System]        FileModifyDate                  : 2024:06:06 12:00:00-07:00
[QuickTime]     Duration                        : 5.27 s

C:\>exiftool -G1 -a -s "-testname<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'));ShiftTime('-6:1:47');DateFmt('%y%m%d %H%M%S%%-c.%%e')}"  Y:\!temp\Test1.mp4
'Y:/!temp/Test1.mp4' --> 'Y:/!temp/240606 055808.mp4'
    0 image files updated
    1 image files unchanged
I was getting weird numbers when I kept the -globalTimeShift and I faintly recall something about it, but can't find the post atm.

[Phil Harvey]

Ah yes.  Using DateFmt does the trick, but the expression gets very complicated.

- Phil

[StarGeek]

Ah yes.  Using DateFmt does the trick, but the expression gets very complicated.

Yes, and I hate messy commands like this. It becomes too easy to make a mistake or type and gets hard to figure out if you forget about it and then need to edit it.

[John Derbyshire]

Thank you both so much for your help on this and actually getting it working! I was looking into the sidecar file option in the meantime but I much prefer this one-step approach

So the final Command Prompt command that I used (i.e. to actually do the renames) is as follows:

exiftool -G1 -a -s "-Filename<${FileModifyDate;ShiftTime('-0:0:'.$self->GetValue('Duration','ValueConv'));ShiftTime('-6:1:47');DateFmt('%y%m%d %H%M%S%%-c.%%e')}" *.MP4