1080p Full HD means 1920 by 1080 pixels. It suits watching on a TV or computer screen, and anything you plan to edit.
Roughly 10 to 15 MB per minute, depending on how much movement the clip contains. That number moves with how much the clip is moving: a static talking head compresses far better than a fast pan or a sports clip, so two videos of the same length at the same resolution can differ in size by a factor of three.
Most X videos top out at 1080p, which is the ceiling for ordinary uploads. 720p halves the file size and is genuinely difficult to distinguish on a phone-sized screen, which makes it the sensible default when you are saving over mobile data. 480p exists for slow connections and for archiving many clips without filling a drive.
The difference is easiest to see on a large screen and hardest to see on a small one. If you plan to edit the clip, or put it on a television, take the highest resolution offered. If you are watching it once on a phone, the smaller file is usually the better trade.
The list of resolutions comes from the post, not from a menu. If a video was uploaded at 720p, there is no 1080p version of it anywhere, and the option will not appear.
This is the point where most downloaders quietly upscale instead, offering a 1080p or even 4K button that stretches a smaller video to fit. The result is a bigger file with no extra detail, because the missing pixels are invented rather than recovered. That is not something this tool does. If 1080p Full HD is offered on a post, it exists in the original.
You get an MP4 holding H.264 video and AAC audio, which is the same file X serves to its own apps. It is copied rather than converted, so there is no second generation of compression loss and no watermark added on the way through.
X itself re-encodes everything uploaded to it, so the source already sits one generation below whatever the poster originally recorded. No downloader can undo that. What a downloader can do is avoid making it worse, and copying rather than re-encoding is how.
The process is identical on mobile. Copy the post link from the X app with the share button, open this page in your browser, and paste it. On iPhone and iPad the file lands in the Files app under Downloads, ready to move into Photos. On Android it goes to the Downloads folder and generally appears in Gallery or Google Photos soon after.
At 1080p Full HD, file size is worth a thought on mobile data. Roughly 10 to 15 MB per minute, depending on how much movement the clip contains. If you are on a metered connection, dropping one step down the list will roughly halve that.
Saving a public video to watch offline, to keep a copy of something you posted, or to quote under fair use is ordinary use. This tool only ever reads what is already public, and keeps no copy once your download finishes.
Redistribution is where it changes. The person who posted the video owns it, and downloading at any resolution does not transfer that. Re-uploading someone else’s work as your own is a copyright problem no matter how the file was obtained.