What "720p" means for vertical videos
Resolution names such as 720p and 1080p count the short side of the picture. A landscape 1920×1080 video is 1080p and a vertical 1080×1920 phone video is also 1080p, so downscaling the vertical one to 720p gives 720×1280. Tools that set the height to 720 produce a squashed 406×720 instead; this one checks the orientation, including rotation flags from iPhones.
Width and height are rounded to even numbers, which H.264 requires, so the aspect ratio may shift by at most one pixel.
Which resolution for which use
- 1080p: TVs and computer screens; the most a phone screen can show.
- 720p: phones, chat apps and email; looks the same as 1080p on most phones.
- 480p: small previews and slow connections.
- 360p: the smallest readable size, for very tight size limits.
4K → 1080p keeps a quarter of the pixels and is the biggest single saving for phone videos that will never be watched on a 4K screen.
Why smaller resolution can look better
At a fixed file size, fewer pixels mean more bits for each one. A clip at 720p and 3 Mbps usually looks cleaner than the same clip at 1080p and 1.6 Mbps, which smears in motion. That is why the target-size tools lower resolution first when bits run short.
Downscaling never adds detail, and the tool never upscales: if the source is smaller than your choice, it keeps the source size.
Rotation and orientation
Without resizing, a phone video keeps its rotation flag and the player turns it. When resizing, the turn is applied to the pixels, so the result is upright in every player, including older ones that ignore rotation flags.