发一点点视频方面的基础知识，E文的

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Coding Ranges
8 or 10 bits per sample are used for each of the YCbCr or R’G’B’ components.
At least two additional bits of fractional YCbCr or R’G’B’ data were desirable to reduce rounding effects when transmitting between equipment in studio editing equipment. For these reasons, most pro-video equipment uses 10-bits YCbCr or R’G’B’, allowed 2 bits of fractional YCbCr or R’G’B’ data to be maintained.
As the Y had a greater margin for overloads at the white levels, as white level limiting is more visible than black. Thus, the nominal 8 bits Y levels are 16-235, while the nominal 8 bits CbCr levels are 16-240.
For 8 bit system, the value of 00H and FFH are reserved for timing information. For 10 bits system 000H-003H and 3FCH-3FFH are reserved for timing information.

SDTV Sample Rate
13.5MHz sample rate for Y, one-half for Cb and Cr, the sample rate is 6.75MHz.
Now the 4:2:2 is commonly used, that Y, U and V were sampled at 4x, 2x and 2x the color subcarrier frequency, respectively.
Adapted to BT.601, that the sampling frequencies of Y, Cb and Cr were 4x, 2x and 2x 3.375MHz, respectively.
With 13.5MHz sampling, each scan line contains 858 samples (480i) or 864 (576i) and consists of a digital blanking interval followed by an active line period.
Both the 480i and 576i use 720 samples during the active line period. With a sample rate of 6.75MHz for Cb and Cr(4:2:2) each active line period contains 360 Cr samples and 360 Cb samples.
BT.601 supported only 480i and 576i system with a 4:3 aspect ratio (720x480i and 720x576i active resolutions). Support for a 16:9 aspect ratio was then added (960x480i and 960x576i active resolutions) using and 18MHz sample rate.

EDTV Sample Rate
The sample rate is doubled to 27MHz(4:3 aspect ratio) or 36MHz(16:9 aspect ratio)

HDTV Sample Rate
In order to keep a static orthogonal sampling grid, each frame rate uses a different sample clock rate.

480i and 480p Systems
Interlaced Analog Composite Video
The 480i system typically 480 active scan lines per frame and they are interlaced. The frame rate is usually 29.97Hz(30/1.001).
The 525 lines per frame with active video present on line 23-262 and 286-525.
Interlaced Digital Component Video
960x480i 18MHz 29.97 Hz
720x480i 13.5MHz 29.97 Hz
Other common active resolutions, their 1x sample rates (Fs), and frame rate,
864x480i 16.38MHz 29.97Hz
704x480i 13.50MHz 29.97Hz
640x480i 12.27MHz 29.97Hz
544x480i 10.12MHz 29.97Hz
528x480i 9.900MHz 29.97Hz........

Progressive Digital Component Video
960x480p 36MHz 59.94Hz
720x480p 27MHz 59.94Hz
Other common active resolutions, their 1xY and R’G’B’ sample rates (Fs) and frame rate
864x480p 32.75MHz 59.94Hz
704x480p 27.00MHz 59.94Hz
640x480p 24.54MHz 59.94Hz
544x480p 20.25MHz 59.94Hz
528x480p 19.80MHz 59.94Hz…..

SIF and QSIF
SIF is defined to have an active resolution of 352x240p. Square pixel SIF is defined to have an active resolution of 320x240p.
QSIF is defined to have an active resolution of 176x120p. Square pixel QSIF is defined to have and active resolution of 160x120p.



576i and 576p Systems
Interlaced Analog Component Video
Analog component signals are comprised of the three signals, analog R’G’B’ or YPbPr.
The frame rate is usually 25 Hz, the analog interface uses 625 lines per frame, with active video present on lines 23-310 and 336-623.

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