[This is preliminary documentation and subject to change.]
The recommended way of deinterlacing and displaying NTSC video, or NTSC video encoded to MPEG, is to show each 720 x 240 x YUV field at 60 hertz on the SVGA screen. This display uses vertical and horizontal interpolation to get at least a full-frame image, that is a 720 x 480 x YUV image.
In this display, the alternating odd and even fields should be shown such that the odd fields are offset by one scan line from the even fields after scaling. Every other field is offset to get rid of image jitter when switching from one field to another. Cropping the extra top and bottom line of the offset fields is also recommended. This sequential display of offset odd and even fields on a 60-hertz (Hz), progressive scan SVGA monitor, running at 800 x 600 or greater resolution, simulates the way video fields appear on a traditional television screen that employs interlacing.
Each field is captured in the display buffer as a 720 x 240 x YUV, 2-byte video plane. The digital to analog converter (DAC) should perform interpolation. To do so, in the DAC a line store buffer that has first in, first out (FIFO) format is loaded. This buffer interpolates the lines of a field as the field is being output. Each video plane requires 345,600 bytes; two planes require 675 kilobytes of video memory.
Double buffering is required to prevent the user from seeing incomplete images, which occurs with a single buffer being updated as it is being output. The double buffers are swapped at the start of the vertical blanking interval (VBI) if and only if a new buffer has been filled with YUV data.
The fields are offset by one scan line, and the "extra" line on each field should be cropped. This cropping is performed because the extra line is only shown at 30 hertz, whereas the rest of the lines are refreshed at 60 hertz. The monitor should be run at 800 x 600 resolution at 60 hertz. This functionality means the fields are often stretched to fill the full display area but are sometimes shrunk, such as when video is displayed in a window.
Note that if a single horizontal line appears on only one field of the display surface, it flickers. All televisions have this problem with NTSC fields. The interlaced approach, though it produces this flicker, avoids various unpleasant artifacts such as feathering, tearing, and odd-field discarding.