Video

Video is a technology that records, transmits, and displays moving images. The images may be recorded onto some medium such as videotape. The recorder may be a separate machine such as a videocassette recorder (also called a VCR) or built into something else such as a video camera. A popular 20th century videotape format was VHS. It was used by many people to record television programmes onto cassettes. This is usually an analog format. In the 21st century digital recording is used more often than analog recording. By extension, a video clip is a short movie. A music video usually stars someone who recorded an (audio) album. One purpose is to promote the album.

Making and showing video

Video is made using a video camera. A camera is an electronic device that takes light from the real world and makes it into pictures. A video camera is like a camera, but takes many pictures very fast to make it a video.

Video is shown with a screen. A screen can either be a monitor, a projector, or a television. The purpose of a screen is to turn video information into light.

History

Analog video

When video technology was first made, it was made for televisions. At first, it was for mechanical televisions, but then cathode-ray tube televisions became more common. The technology was analog.

Digital video

Digital video came after analog video. At first, the digital video was not useful because the bitrate (how quick a picture moves through a wire) was too high. After data compression was made, digital video became more useful than analog video.

Properties of video

Frames per second

Frames per second is a number which means how quick a picture is shown to a person watching the video. Videos are just pictures shown one by one, but very very fast. So the frame rate is the number of pictures that are shown in 1 second.

Interlaced and progressive

A video can be interlaced or progressive. When a picture is shown in a video, it is divided into many lines.

In a progressive video, The screen will draw each line one by one from the top of the picture until the bottom of the picture.

But in an interlaced video, the screen will only draw the odd lines at first. So the screen will draw 1, 3, 5, 7, until it touches the bottom. When it does, the screen will go to the second line, and draw the even lines.

Aspect ratio

A video has an aspect ratio. An aspect ratio gives the shape of a video. The video can either be a square or a rectangle. To get the aspect ratio, you divide the width by the height. Then you write it as a ratio.

A video shaped like a square has an aspect ratio of 1, because the width and height are the same number.

A video which is a rectangle has an aspect ratio that is not 1. A video that is tall has an aspect ratio where the right side of the ratio is bigger. But a video that is wide has an aspect ratio where the left number is bigger.

Common aspect ratios are 16:9 and 4:3.

Color information

The pictures in a video have color information. For every pixel in the picture, which is a small box which is part of the picture, there is a color. This color can be put inside the video using a color model