Video Sampling

The on-board video decoder digitizes the analog video signal using the YUV 4:2:2 sampling method. The luminance component Y is sampled at 13.5 MHz, and the chrominance components U and V are sampled at half-frequency at 6.75 MHz. The sampling rates are identical for both 625-line and 525-line television systems.

The sampling rates are not adjustable, the actual luminance sampling rate is proportional to the line frequency of the video signal, in order to produce a fixed integer amount of samples per line. There are 858 samples per line in case of 525-line television systems, and 864 samples per line in case of 625-line television systems. The sampling clock is a phase-locked on the falling edge of the sync tip.

The sample aspect ratio is about 11/10 for 525-line system, and about 54/59 for 625-line system.

Digital Active Area

The digital active area is a rectangular area of digitally active samples. Its size and position depend on the actual television system of the video signal.

Digital Active Area (625-line television system)

For 625-line television system, the size and position of the digital active area is shown in the next figure.

V16H264DigitalActiveArea625One

Digital active area definition — 625-line system
One frame after scan conversion (spatial line ordering)

V16H264DigitalActiveArea625Two

Digital active area definition — 625-line system
Two successive fields before scan conversion (temporal line ordering)

The digital active area size and position are defined according to ITU-R BT.601 standard.

The analog active width is about 18 pixels narrower than the digital active width, leaving a blanked margin of 8~9 pixels on the left and right sides. The first and the last lines of the digital active area contain partial video lines.

Digital Active Area (525-line television system)

For 525-line television system, the size and position of the digital active area are shown in the next figure.

V16H264DigitalActiveArea525One

Digital active area definition — 525-line system
One frame after scan conversion (spatial line ordering)

V16H264DigitalActiveArea525Two

Digital active area definition — 625-line system
Two successive fields before scan conversion (temporal line ordering)

The digital active area size and position are defined according to ITU-R BT.601 standard.

The digital active height and the vertical position are defined according to SMPTE recommended practice RP-202, "Video Alignment for MPEG coding". The digital active area includes the 240 lowest full lines of each field, for a total of 480 lines.

The analog active width is about 9 pixels narrower than the digital active width, leaving a blanked margin of 4~5 pixels on the left and right sides.