Do you know all the knowledge about video?

720P, 1080P, 4K, MP, etc. Often used to denote the resolution of a video, but with so many claims it can be confusing and confusing. Now take you to understand their specific meaning:

"P"

720P and 1080P represent the total number of video pixels. For example, 720P means that the video has 720 lines of pixels, and 1080P means that the video has a total of 1080 lines of pixels. The number of pixels of a 1080P resolution camera is 1920*1080. "P" (short for Progressive) itself means "progressive scan". Today's cameras are basically in progressive scan mode. Compared to interlaced scanning, "p" has little meaning.



"K"

2K, 4K, etc. Means "total columns of video pixels"; for example, 4K means the video has 4000 columns of pixels, 3840 or 4096 to be exact. There are two types of 4K resolution camera pixels, the first is: 4096*2160; the second is: 3840*2160.



"MP"

MP stands for the total number of pixels, and refers to the result (megapixels) obtained by multiplying the number of rows (P) and columns (K) of pixels.

In HD network cameras, we usually call them mega or two megapixel cameras:

The resolution of 1080P is 1920*1080 pixels, and the actual pixel is 2073600, so people usually call 1080p or 1080i 2 million pixels resolution;

The resolution of 90p is 1280*960 pixels, and the actual pixel is 228,800, so people usually call 960P or 960i a resolution of 1.3 million pixels;

The resolution of 720P is 1280*720 pixels, and the actual pixel is 921600, so people usually call 720p or 720i megapixel resolution.

Code stream:

Data rate, also known as bit rate, refers to the data stream used by video files per unit of time, and plays an important role in video encoding quality control. Under the same resolution, the larger the video file stream, the smaller the compression ratio and the better the picture quality. Almost all encoding formats pay more attention to how to achieve the least distortion at the lowest bit rate.



Mainstream and substreams:

In general high-definition camera products, the encoder can produce two different encoding formats at the same time. We refer to these two encoding formats collectively as the main bitstream and the sub-bitstream. The main stream is used for local storage, and the sub-stream is suitable for image transmission on low-bandwidth networks. The advantage of dual-stream technology is that both high-quality image transmission and narrow-bandwidth transmission are taken into account, meeting the requirements of local transmission and remote transmission.

Dual stream adopts high bit rate stream for local high-definition storage, such as QCIF/CIF/D1 encoding. Considering local storage and remote network transmission, low bit rate streams are used for network transmission, such as QCIF/CIF encoding.

Knowing the above theory, you should understand why people on the Internet often ask questions like this:

Why does video surveillance use substream images or blur?

Why does the webcam use the main stream to drag the screen, but there is no problem with the sub stream?

The above two problems are because the main stream is the mode with the highest pixel resolution, and the sub-stream is the mode with low pixel resolution and low resolution!



Frame rate:

Frame rate refers to the number of images per second, and one frame represents a still picture. Consecutive frames form an animation. A high frame rate results in smoother, more realistic animations, such as TV images. The number of frames we usually say refers to the number of frames transmitted in one second. The more frames per second (fps), the smoother the motion displayed.

The difference between H.264 and H.265

Both H.264 and H.265 are reference video coding standards. H265 reduces the bit stream while maintaining clarity. That is to say, for general monitoring systems, H.265 can save storage space and reduce network bandwidth. Therefore, the application of H.265 technology not only reduces the storage cost of hard disks, but also reduces the cost of switches.

It should be noted that old cameras connected to H.265 recorders cannot save storage space. For IP cameras and video recorders, both parties must support H.265 technology to achieve the above functions. If one party supports H.265, because it is backward compatible, except that the storage cannot be halved, other functions are normal.