How does interlaced video use less bandwidth?

Basic vocabulary of the scan type

Progressive video

Progressive videocontains all lines in all frames. It looks better on modern screens because it drastically reduces the amount of image flicker that the viewer sees on the screen. Devices displaying progressive video redraw all horizontal lines in a frame. For example, a 50 Hertz device playing 1080 progressive video redraws 1080 lines (each line in the frame) 50 times per second.

Interlaced video

Interlaced videouses a technique that doubles the perceived frame rate of a video ad without consuming additional bandwidth. On older screens, most people do not notice degraded video quality with interlaced video. Devices that support interlaced video will all redrawEASTERhorizontal line in a frame. For example, a 50 Hertz device playing 1080 interlaced video draws 540 lines (half the lines in the frame) 50 times per second.

Field polarity for interlaced frames

Interlaced video contains two fields of a video image, each made up of every other horizontal line in the image. polarityin video distinguishes between these two sets of lines. The polarity of a sentence indicates whether the top field comes first or the bottom field comes first. In the following figure, the set with polarity of the top field is shown in blue and contains the top line. The sentence with polarity of the lower field is shown in red and contains the second horizontal line from the top. The complete frame contains both, with each set being updated alternately.

When creating interlaced output with MediaConvert, you can specify which field polarity first with the settingInterlace modeout.