720p is a video display format. The letter p means progressive scan, and the number 720 means that there are 720 scan lines in the horizontal direction. Generally, the resolution of 720p is 1280×720, which can also be called high definition (HD). However, in some cases, such as iPod Touch 4, its 720P video recording does not refer to 1280×720 (16:9), but 960×720 (4:3), so 720P video recording without HD is not all Refers to 1280×720 (16:9).
System Total scan line Image area scan line Horizontal total pixels Image area horizontal pixels Sampling frequency
1080P / 60Hz 1125 1080 2200 1920 148.5MHz
1080P / 50Hz 1125 1080 2640 1920 148.5MHz
1080I / 60Hz 1125 1080 2200 1920 74.25MHz
1080I / 50Hz 1125 1080 2640 1920 74.25MHz
720P / 60Hz 750 720 1650 1280 74.25MHz
720P / 50Hz 750 720 1980 1280 74.25MHz
The basic concept of digital video is derived from analog video. For analog video, we can understand it like this:
The video can be decomposed into several basic viewpoints (pixels), and each pixel has independent color information. Use an electron gun to print out these points in rows and columns on the screen to form a complete picture, which is continuously output. , The use of the delay characteristics of the human eye can display "dynamic" images.
Analog bandwidth: also known as "dot clock", refers to the number of pixels scanned per second, that is, the total number of frequency points displayed on each scan line in a unit time, in MHz in analog video.
For example, the analog bandwidth of 720P/60Hz = 1650 * 750 * 60 = 74.25MHz means that each clock must transmit 74.25M analog video pixels. Similarly, the dot clock of 1080P60 is 148.5MHz.
But in digital video, each pixel is represented by 3 different colors, and each color is transmitted by a certain number of bits. Therefore, bps is usually used to represent the digital bandwidth. If RGB is used for transmission, each color is 1 byte to output, then the digital bandwidth of the video is:
Digital BandWidth = analog bandwidth * 8bit * 3 = 1.782Gbps means that 1.782 G bits of data are transmitted per second.
1782 / 24 = 74.25
2640 * 1125 = 2970000 * 50 = 148500000 * 8 * 3 = 3564000000 = 3.564 Gbps
2200 * 1125 = 2475000 * 60 = 148500000