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iOS: recorded video location is written without ISO 6709 fixed-width degrees, Photos drops it

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
80/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
swift
Domain
mobile

Research direction

The fix lives in ios/Extensions/CoreLocation/CLLocation+toISO6709String.swift, where latPart and lonPart are formatted with %+.Nf around the normalizeNegZero calls. Start there and change the format so the degrees are zero-padded to fixed widths (2 for latitude, 3 for longitude), keeping the fraction digits. Done when a recorded video's com.apple.quicktime.location.ISO6709 item reads a padded string such as +48.838800+002.378600/ and Photos places it on the map.

Written by the indexing model from the issue text.

Description

Prerequisites
  • I have read and followed every applicable step in the Nitro Modules Troubleshooting guide.
  • I have read the VisionCamera Troubleshooting guide.
  • I have searched existing issues and found nothing matching.
  • I am on the latest version of react-native-vision-camera (5.2.3).
What happened

A video recorded with createRecorder({ location }) on iOS carries its position in the com.apple.quicktime.location.ISO6709 metadata item, but the string is written without the fixed-width degrees ISO 6709 Annex H requires. CLLocation+toISO6709String.swift formats both coordinates with "%+.\(fractionalDigits)f", so a position in Paris becomes +48.838800+2.378600/.

Apple's own QuickTime example is +27.5916+086.5640+8850/: two digits for the latitude degrees, three for the longitude degrees, zero-filled. When the longitude (or the latitude) has fewer digits than that, the Photos library drops the whole location on import: the video shows no place on the map and no location in its info panel. Any video shot at a longitude between -10° and 10° (Western Europe, West Africa, the UK…) or a latitude between -10° and 10° is affected. The same file with the padded string (+48.838800+002.378600/) is placed correctly.

Steps to reproduce
  1. On iOS, record a video with createRecorder({ location }), with the device in Paris (or any position with a longitude between -10° and 10°, e.g. a simulated 48.8388, 2.3786).
  2. Save the resulting file to the camera roll (PHPhotoLibrary / expo-media-library).
  3. Open the Photos app on the video.
What did you expect to happen?

The video is placed on the map in Photos, like one recorded by the Camera app.

What actually happened?

Photos shows no location for the video. The file's com.apple.quicktime.location.ISO6709 item reads +48.838800+2.378600/.

Fix

Give the degrees their fixed width, zero-filled (sign + 2 digits for the latitude, sign + 3 for the longitude, plus the fraction). This is the patch we ship through pnpm patch:

--- a/ios/Extensions/CoreLocation/CLLocation+toISO6709String.swift
+++ b/ios/Extensions/CoreLocation/CLLocation+toISO6709String.swift
@@ -34,9 +34,13 @@ extension CLLocation {
     let latN = normalizeNegZero(lat)
     let lonN = normalizeNegZero(lon)

-    // No field widths needed; the important part is forced sign and fixed fraction digits.
-    let latPart = String(format: "%+.\(fractionalDigits)f", latN)
-    let lonPart = String(format: "%+.\(fractionalDigits)f", lonN)
+    // ISO 6709 Annex H gives the degrees a fixed length, zero-filled: two digits for the latitude,
+    // three for the longitude, as in Apple's QuickTime example "+27.5916+086.5640+8850/". The Photos
+    // library drops the whole tag otherwise: a video shot at longitude "+2.378600" (Paris) or
+    // latitude "+7.046953" is imported without a location.
+    let fractionWidth = fractionalDigits > 0 ? fractionalDigits + 1 : 0
+    let latPart = String(format: "%+0\(3 + fractionWidth).\(fractionalDigits)f", latN)
+    let lonPart = String(format: "%+0\(4 + fractionWidth).\(fractionalDigits)f", lonN)

     var s = latPart + lonPart

Happy to open a PR with it if you want.

Affected platforms
  • iOS
  • Android
Device(s) affected

iPhone; the unpadded tag is also visible on the simulator by saving the file and inspecting it.

VisionCamera version

5.2.3

React Native version

0.86.3 (Expo SDK 57)

React Native architecture

New Architecture (Nitro)

Features being used
  • Video capture
Dominant language
TypeScript
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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