Stored in the EXIF metadata, which tracks exactly when and where (if GPS was on) the video was taken.
It is commonly seen in public iCloud or Google Photos links shared on social media, typically showing personal events like concerts, sports, or family gatherings. Potential Metadata for a file named "IMG_7835.MOV"
A user uploaded a video with this name (as an .MP4 variant) to demonstrate a technical bug with brushes and fill layers in Affinity Photo.