Video `Create Date` with GPS inferred timezone

[jrasm91]

It does not seem possible to get a correct Create Date with a GPS inferred timezone for a video that is using UTC.

Example

File

$ exiftool PXL_20210906_174416840.mp4

Create Date                     : 2021:09:06 17:44:16
...
GPS Latitude                    : 33 deg 21' 11.16" N
GPS Longitude                   : 111 deg 51' 46.08" W
GPS Position                    : 33 deg 21' 11.16" N, 111 deg 51' 46.08" W

Options

const { exiftool } = require('exiftool-vendored');

async function test(filename, options) {
  const tags = await exiftool.read(filename, undefined, options);
  return {
    ...options,
    CreateDate: tags.CreateDate.toString(),
    tz: tags.tz,
  };
}

async function run() {
  const filename = 'File1.mp4';
  console.table([
    await test(filename, { defaultVideosToUTC: false, backfillTimezones: false, inferTimezoneFromDatestamps: false }),
    await test(filename, { defaultVideosToUTC: false, backfillTimezones: false, inferTimezoneFromDatestamps: true }),
    await test(filename, { defaultVideosToUTC: false, backfillTimezones: true, inferTimezoneFromDatestamps: false }),
    await test(filename, { defaultVideosToUTC: true, backfillTimezones: false, inferTimezoneFromDatestamps: false }),
    await test(filename, { defaultVideosToUTC: true, backfillTimezones: false, inferTimezoneFromDatestamps: true }),
    await test(filename, { defaultVideosToUTC: true, backfillTimezones: true, inferTimezoneFromDatestamps: false }),
    await test(filename, { defaultVideosToUTC: true, backfillTimezones: true, inferTimezoneFromDatestamps: true }),
  ]);
}

run().then(() => process.exit());

Results

(index)	...ToUTC	backfill...	infer...	CreateDate	tz
0	false	false	false	'2021-09-06T17:44:16-07:00'	'America/Phoenix'
1	false	false	true	'2021-09-06T17:44:16-07:00'	'America/Phoenix'
2	false	true	false	'2021-09-06T17:44:16-07:00'	'America/Phoenix'
3	true	false	false	'2021-09-06T17:44:16Z'	'UTC'
4	true	false	true	'2021-09-06T17:44:16Z'	'UTC'
5	true	true	false	'2021-09-06T17:44:16Z'	'UTC'
6	true	true	true	'2021-09-06T17:44:16Z'	'UTC'

• When defaultVideosToUTC is false, the timezone from GPS is correct, but the time is now wrong.
• When defaultVideosToUTC is true, the timezone is time is correct, but the GPS timezone is not used.
• The time and timezone is actually correct when using the file from #113 and all three options set to true (has additional Creation Date with a timezone)

Expected Value

When defaultVideosToUTC is used with backfillTimezones and GPS data is available, I expected tz to be populated from GPS (America/Phoenix) and CreateDate to be adjusted for said timezone (2021-09-06T10:44:16-07:00).

[mceachen]

Thanks for this research. Is this video metadata directly from a smartphone, or was it edited?

If you could attach all date and time fields coming from exiftool for that file, or just attach the file itself, that might be helpful for me to replicate your table.

(Fwiw, I would have expected defaultVideosToUTC: false, backfillTimezones: true to do what you wanted)

[jrasm91]

It's directly from the phone. In general, I don't think any of the videos from my pixel phones have timezone information in them.

Here's the file: File1.zip

Here's *Date* properties:

jrasm91@jrasm91-ubuntu:Videos$ exiftool -*Date* File1.mp4 
File Modification Date/Time     : 2022:10:26 19:56:17-04:00
File Access Date/Time           : 2023:09:13 13:22:13-04:00
File Inode Change Date/Time     : 2023:09:13 13:21:46-04:00
Create Date                     : 2021:09:06 17:44:16
Modify Date                     : 2021:09:06 17:44:16
Track Create Date               : 2021:09:06 17:44:16
Track Modify Date               : 2021:09:06 17:44:16
Media Create Date               : 2021:09:06 17:44:16
Media Modify Date               : 2021:09:06 17:44:16

Full exif dump

``` ExifTool Version Number : 12.40 File Name : File1.mp4 Directory : . File Size : 4.7 MiB File Modification Date/Time : 2022:10:26 19:56:17-04:00 File Access Date/Time : 2023:09:13 13:22:13-04:00 File Inode Change Date/Time : 2023:09:13 13:21:46-04:00 File Permissions : -rwxr-xr-x File Type : MP4 File Type Extension : mp4 MIME Type : video/mp4 Major Brand : MP4 v2 [ISO 14496-14] Minor Version : 0.0.0 Compatible Brands : isom, mp42 Media Data Size : 4940337 Media Data Offset : 40 Movie Header Version : 0 Create Date : 2021:09:06 17:44:16 Modify Date : 2021:09:06 17:44:16 Time Scale : 10000 Duration : 2.97 s Preferred Rate : 1 Preferred Volume : 100.00% Preview Time : 0 s Preview Duration : 0 s Poster Time : 0 s Selection Time : 0 Audio Format : mp4a Audio Channels : 2 Audio Bits Per Sample : 16 Audio Sample Rate : 48000 Matrix Structure : 0 1 0 -1 0 0 0 0 1 Media Header Version : 0 Media Create Date : 2021:09:06 17:44:16 Media Modify Date : 2021:09:06 17:44:16 Media Time Scale : 90000 Media Duration : 0 s Handler Type : NRT Metadata Handler Description : MetaHandle Meta Format : mett Image Size : 1024x768 Megapixels : 0.786 Avg Bitrate : 13.3 Mbps GPS Latitude : 33 deg 21' 11.16" N GPS Longitude : 111 deg 51' 46.08" W Rotation : 90 GPS Position : 33 deg 21' 11.16" N, 111 deg 51' 46.08" W ```

[mceachen]

OK, I just checked the relevant code again, and these settings should indeed work.

Here's the validation spec:

https://github.com/photostructure/exiftool-vendored.js/commit/22fe14924ca77105bfa6270c57b7a0c6165c9041

[mceachen]

Ah -- I misread your expectations: you want both the timezone to default to UTC, and the timestamps to be shoved to Phoenix. Gotcha.

Poking the code with a stick now.

[jrasm91]

Yeah, it's the combination of "don't mess up the timestamp because it is a video" and "please convert it from UTC to X using GPS"

[mceachen]

Currently backfillTimezones is conservative: it doesn't set the time zone for ExifDateTime instances that already "have a zone".

Unfortunately, there isn't a discriminator for those ExifDateTime instances that are UTC because of #defaultToUTC, or because their raw value actually included a zone offset.

Edit: I just added the discriminator, so we can make this change safely now.

[mceachen]

OK, I think this warrants a major release, as the output will be different for people using backfillTimezones.

[mceachen]

Pushed. I'll release as soon as GHA validates the tests pass. Details here:

https://github.com/photostructure/exiftool-vendored.js/blob/main/CHANGELOG.md#v2300

https://github.com/photostructure/exiftool-vendored.js/commit/fbabbce474631559d81b8625293d1886592e8890

[mceachen]

released v23.0.0 :tada:

[jrasm91]

Perfect! Thank you for working on this an the fast turn around time. I just wanted to confirm that I've tested against v23 and everything is working as expected. :pray: