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What is the code rate? Part 3

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What is the code rate? Part 3

code rate

Video imaging methods are mainly divided into two types: interlaced scan and progressive scan.

code rate

In plain and simple terms, an image (a frame) is made up of lines made up of hundreds of rows of pixels.

Interlacing means that only half of the lines are displayed on one screen at a time, and is made up of odd or even lines, displayed alternately with each other. It is commonly said “i”.

Originally, the image the TV would transmit per second was set to 50 frames per second. Think that the image does not flash in our eyes. However, according to the technology at the time, it was difficult to achieve 50 frames per second of TV transmission. Scientists used the persistence of human vision to invent interlaced transmission.

Interleaving is a technology developed to transmit television signals using limited bandwidth. In an interlaced system, only half the number of horizontal lines per video frame is transmitted at a time. The viewer can perceive each frame at full resolution due to transfer speed, display persistence, and persistence of vision. All analog TV standards use interlace technology. Digital television standards include interlaced and non-interlaced technologies.

(The above is official Adobe content)

We all use no field (line by line) now

video ratio

Video ratio refers to the ratio of the length to width of the video screen played by the video player. The ratio between the length and width of the CRT television used in ordinary homes is 4:3, that is, the video ratio is 4:3. The high-definition screen video ratio (TV and mobile) that is currently being developed is 16:9. The current full screen mobile phone is 17: 9

Due to the development and application of various screens, video production is also relatively informal, and will be adjusted according to the requirements of Part A, such as large conference screens and advertising screens.

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What is the code rate? Part 2

Code Rate

Generally speaking, there are only a few common frame numbers that we use to make videos: 24 frames, 25 frames, 29.97 frames, and 30 frames.

code rate

Different areas and different uses require different frames.

Frames per second

Frame rate is also known as the abbreviation FPS (Frames PerSecond): frames per second. It refers to the number of image frames that are updated per second, which can also be understood as the graphics processor can update multiple times per second. The more frames per second (FPS), the smoother the motion is displayed. When capturing dynamic video content, the higher the number, the better.

If the frame rate exceeds the refresh rate of the screen, it only wastes graphics processing power, because the monitor cannot refresh as fast, so the frame rate that exceeds the refresh rate is wasted.

For games, in general, first person shooters pay more attention to the FPS level, if FPS is <30, the game will seem inconsistent. So, there is an interesting saying: “FPS (referring to FPS games) focuses on FPS (referring to frame rate).

The frame rate is not as high as possible. Most common mobile phone recording frame rates on the market are 30fps, TV 25/30 (common use) 50/60fps, etc. (sports shots), high-speed cameras 120/240 fps (slow motion)

iphone7 camera parameters

Resolution

Resolution, also known as resolution and resolution, can be classified into two directions: screen resolution and image resolution.

Screen resolution (screen resolution) is the accuracy of the screen image and refers to how many pixels a monitor can display.

What is the code rate?

What is the bit rate for? What is frame rate? What is the resolution?

Students often ask, what is the code rate? What is the bit rate for? What is frame rate? What is the resolution?

This problem of not being able to speak clearly, listening and not understanding has worried many beginners.

Today Ben Shuai specially came to solve these professional terms for you.

frame

In the video, do you know what the unit less than a second is?

That’s right, it’s what I’m going to talk about today: “framework”!

Frame: It is the smallest unit in video animation and countless frames constitute seconds.

Simply put, one frame equals one image, and a second is made up of a certain frame, that is, a certain number of images!

Play the images continuously and you will see dynamic images under the influence of the visual residue produced by your eyes.

The more frames per second, the smoother and more realistic the images we see!

We also call the number of frames in 1 second the number of frames, usually expressed in fps (FramesPer Second).

Bit rate, what is it?

Bit rate, what is it?

as a feature of digital audio and video

Bitrate: literally, the information bit rate. It is common to use the bit rate when measuring the effective information transmission rate through the channel, that is, the “payload” transmission rate (in addition to that, the channel can transmit service information, for example, start and stop symbols for asynchronous transmission or control symbols for redundant coding). The baud rate, which takes into account the total bandwidth of the channel, is measured in baud.

Bit rate is the number of units of information required to store (transmit) one second of a stream of data (generally audio and video files). It is generally measured in ‘kbps’, kilobits per second.

The term bit rate is used in two basic meanings
: channel or device characteristic: the maximum number of bits that can be transmitted per unit of time.
– The size of the data stream transmitted in real time (the minimum size of the channel that can pass this stream without delay).
– A special case is the compressed video or audio bit rate.
Bitrate is expressed in bits per second (bit / s, bps), as well as values derived with the prefixes kilo, mega, etc.

The term bit rate (in conjunction with subjective quality criteria) is often used as a characteristic to evaluate the performance of lossy compression algorithms.

Bitrate characterizes both the density of the information package and its quality. For example, out of two MP3 files compressed with different bit rates, a file with a higher bit rate will have higher sound quality (close to the original). At the same time, a file of a different format, with the same bit rate, can offer both better and worse sound quality.

On an audio CD, information is losslessly encoded at a constant 1407 kbps bit rate.

The MP3 format allows you to encode audio information with constant or variable bit rates from 32 to 320 kbps, that is, they provide five times the compression compared to CD.

Bit rate as a characteristic of digital video and audio

In streaming video and audio formats (such as MPEG and MP3) that use lossy compression, the bit rate parameter expresses the degree of compression of the stream and therefore determines the size of the channel for which it is compressed data transmission. Most of the time, the audio and video bit rate is measured in kilobits per second (kilobits per second in English – kbps), less often – in megabits per second (for video only).

There are three compression modes for data transmission:

– with a constant bit rate (constant bit rate in English – CBR)
– with a variable bit rate (variable bit rate in English – VBR)
– with an average bitrate (English Average Bitrate – ABR)

Variable and average bit rate

The codec chooses the required bit rate based on the parameters (the level of the desired quality) and, during the encoded chunk, the bit rate may change. When compressing audio, the desired bit rate is determined based on the psychoacoustic model. ABR is a variation of VBR in which the codec is compressed to a specified average value.