A mobile-browser workflow for iPhone and Android
The last step differs by operating system: iOS may require Files > Share > Save Video for a compatible file, while Android exposes the saved item through Chrome's downloads list or a file manager. Neither system can add missing detail by selecting a higher resolution, and unsupported codecs may require another player. Large files consume device storage and need a stable connection, especially over mobile data. Keep the browser available until the download starts, then confirm the saved file in the OS download manager before closing the tab.
A phone can save a video through its built-in browser without installing an additional downloader. On iPhone, Safari typically puts the file in Files; on Android, Chrome usually places it in Downloads and the gallery may index it afterward. YTMetadata presents the formats available for the source URL, including MP4 resolutions when offered. HD streams may consist of separate DASH video and audio tracks that the service muxes into one file. H.264/AAC MP4 is widely supported, but an extension by itself does not guarantee a codec.