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18.104.22.168. Avalon-ST Video Control Packets for 4:2:0 Video
When the Chroma Resampler II IP core receives or transmits an Avalon-ST video carrying a frame in 4:2:0 format, the control packet of the associated frame will have a horizontal resolution that is half the actual resolution of the frame.
The triplet of 2 luma and 1 chroma values in 4:2:0 represent 2 pixels but they are carried in a single “pixel” of symbols in the AV-ST domain. Because the triplet is counted as a single pixel, the value of the horizontal resolution carried in control packets will be half that of the resolution the data actually represents.
For example, a UHD frame received in 4:4:4 will have a control packet specifying 3840x2160. The same resolution frame received in 4:2:0 will have a control packet indicating 1920x2160.
- When converting from 4:2:0 to either 4:2:2 or 4:4:4, the horizontal width will be doubled.
- When converting from 4:4:4 or 4:2:2 down to 4:2:0 the horizontal width is halved.
If you choose to create your own 4:2:0 processing blocks, the half horizontal width control packet requirement must be met.
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