Two-pass encoding

One pass encodes as it goes, guessing at what is coming next. Two-pass reads the entire file first and builds a map of which sections are complex and which are simple, then encodes properly using that map, handing more data to a fast-moving crowd scene and less to a static talking head. At any given file size the result is a cleaner picture, and the gap widens the more the footage varies. It costs roughly double the export time. Worth it on a long upload with mixed material or when a hard size limit is forcing your hand, and pointless on a draft. Export at a high enough bitrate that nothing is straining and both settings look identical.