The process of changing the vertical rate of moving pictures. This has become far more important with the use of HD and UHD with their inclusion of many frame rates in the standards with 23.98P, 24P, 25P, 29.97P, 30P, 50I, 50P, 59.94I, 59.94P, 60I and 60P Hz. Changing from one rate to another, including between interlaced and progressive scans, requires considerable technology to produce high quality results. Further frequencies are used in other media markets, such as mobile and some web-based areas with more restricted bandwidth, where lower rates such as 15 f/s and others are found.
Conversions that simply drop or repeat fields or frames produce poor results – especially where the video includes a lot of motion, e.g. sports. For better results some form of motion compensation is used that analyzes the motion and uses this information to create new images in between those that are coincident between the input and output.