To check the metadata of a video or photo on iPhone, open it in the Photos app and swipe up, or tap the Info button. The panel shows the device that recorded it, camera details such as the lens, shutter speed and file size, a map if a location was saved, and a caption you can type.
That covers what most people want to know, and it works the same for photos and videos. What it leaves out matters when a clip will not play, looks wrong after upload, or you need to know exactly what you are sharing: the codec, the HDR format, the bitrate, the time zone and the dozens of tags Apple writes behind the scenes.
For those, you can open the same file in Safari with metadata.video, which reads it on your iPhone without uploading it and explains every field. This guide covers the built-in route first, then what the full view adds.