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Video resolution
720p (720 lines progressive) is a progressive HD signal format with 720 horizontal lines/1280 columns and an aspect ratio (AR) of 16:9, normally known as widescreen HD (1.78:1). All major HD broadcasting standards (such as SMPTE 292M) include a 720p format, which has a resolution of 1280×720.
720i (720 lines interlaced) is an erroneous term found in numerous sources and publications. Typically, it is a typographical error in which the author is referring to the 720p HDTV format. However, in some cases it is incorrectly presented as an actual alternative format to 720p. No proposed or existing broadcast standard permits 720 interlaced lines in a video frame at any frame rate.
Comparison with interlace scanning
Progressive scanning reduces the need to prevent flicker by anti-aliasing single high contrast horizontal lines. It is also easier to perform high-quality 50<->60 Hz conversion and slow-motion clips with progressive video.
S
Resolution
A/R
HD
960×720p
4:3
HD
1280×720p
16:9
HD
720×1280p
9:16
S=standard A/R=aspect ratio
Notes
It is, however, more commonly broadcast at (60/1.001), or precisely 59.940059, matching the NTSC SDTV field rate; this and the 50.00 Hz of PAL are still the second and third highest standard framerates.