be either 50  Hz  (Europe) or 60  Hz  (USA), except for  1080p , which denotes 1080p24, 1080p25, and 1080p30, but also 1080p50 and 1080p60. A  frame  or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second and 50i means 25 progressive