Basics Of Video

So What is Video?

Video is nothing but a series of still images, displayed fast, one after the other. Each still image is called a frame, and the rate at which the images are displayed are called a video’s frame rate. Since the human eye is only capable of seeing less than 25 different images per second, any video that has a frame rate of 25 frames per second (fps) or more appears to have smooth movement, just as we perceive movement in real life!

If a video displays less than 25 different frames per second (fps), it appears to be jerky, and our eyes can perceive the breaks in movement.

At 25 fps or faster, however, video always looks realistic and smooth. The standard frame rate for analogue video is 25 fps for PAL (Phase Alternation Line) video, and 30 fps for NTSC (National Television Systems Committee) video. PAL and NTSC are the different kinds of video formats we receive TV signals in. Most countries use the standard PAL video format. NTSC is more prevalent in the US.

What Is Analogue Video?

Analogue video transmits or stores video data in a continuous wave of red green and blue (RGB). The signal is varied using different frequencies of each colour’s wave to display changing images at the receiver’s end. Since this format involves an unbroken transmission of wave data, it is prone to noise (distortion). However, since this continuous stream of data is very similar to the way we humans perceive the world-our eyes receive a continuous stream of light waves, which our brain perceives as moving images (video)-analogue video data represents reality better.

What Is Digital Video?

Digital video is nothing more than a series of images, all stored in digital format (ones and zeroes) that is displayed in quick succession on a screen (such as a computer monitor).

A digital video recorder, for example, takes analogue signals (light waves) and records them into a digital representation of the analogue data. So almost all digital video is nothing but a computer’s understanding of analogue video. There are exceptions, such as in the case of, say, games, where there is no analogue data to begin with, and all the data is created and displayed digitally.

Which Is Better?

Though there is no perceivable difference between analogue and digital video to the human eye, digital video is preferred because of the ease with which it can be manipulated.

In order to, say, edit a video, or to store it easily, digital format offers a great advantage. You can just open up a software and start editing your digital video, or store hundreds of movies, or movie clips, on your hard drive, or even make copies of your personal videos and share them easily with your friends or family. With computers in our lives, doing all this has become a no-brainer, for most.

With analogue video, you would need to store each video on a video cassette, and making copies of that cassette would involve two video cassette recorders-one playing back the cassette, and another recording the video in real time on to another cassette which is a very tedious task. With digital video, the same task becomes as easy as copying the video file to another computer or device, or even e-mailing it to hundreds of friends and family members. This is where digital video has the definite upper hand.

Where Do I See Digital Video?

Since we only see through our eyes, and our eyes are analogue video receivers, one could say that you NEVER see digital video at all!

However, we’ll leave such philosophical thoughts behind us within this book and consider only the way in which videos are created, stored, or displayed as the parameters of segregating them into digital or analogue.

Most people don’t realise it, but every second you spend in front of your computer, you are seeing digital video. Every movie or video clip you watch on your computer is digital video; every DVD you pop into the DVD player or DVD-ROM drive is an instance of digital video; the same goes for VCDs, and the MMSes you send and receive; even animated GIF files on the Internet are the same, as are streaming movies or clips. The list is endless.

Even satellite television is transmitted today using digital signals, which are converted to analogue at your cable-provider’s premises, before being transmitted to you. Perhaps our only interaction with analogue video today is when watching a movie in a theatre and when watching or recording videos video cassette players or cameras.

How Does A Computer Display Digital Video?

This is perhaps the most basic of questions that all of us want to know. Let’s start with how a computer displays data on the monitor:

The Monitor

Let’s get to know the computer monitor better first. The most important human interface device in a computer is the monitor, because it is what we humans look at to understand what is currently happening inside our computer system. Even though the computer has no use for text and graphics and works only in terms of ones and zeroes (data), the computer display shows us text and graphics, which our minds are able to understand.

Most of us work with Cathode Ray Tube (CRT) monitors, which are much like the TVs we all have at home. A few of us choose to pay that little extra and opt for Liquid Crystal Display (LCD) monitors (as on laptops).

The words we most often hear when dealing with monitors are “refresh rate” and “resolution”. Here, maximum resolution is the maximum number of dots (pixels) that a monitor can display along its horizontal axis and vertical axis. Thus, a monitor with a maximum resolution of 1024 x 768 can display a maximum of 1024 pixels along its horizontal axis and 768 pixels along its vertical axis.

The refresh rate of a monitor is pretty straight forwardly, the number of times it can draw a whole screen of pixels (1024 horizontal and 768 vertical, in the previous example) per second. So a refresh rate of 85 Hertz (Hz, or number of times per second) at a resolution of 1024 x 768 means that a monitor is drawing the whole screen of 1024 x 768 pixels 85 times per second.

Another term you will come across is wide-screen. In order to explain wide-screen, we first have to talk about aspect ratios: The aspect ratio of a display is the ratio of the number of horizontal pixels to vertical pixels. The most common aspect ratio is 4:3 for most computer monitors. However, in order to display certain games and most DVD movies optimally, the wide-screen display was made.

Wide-screen displays have an aspect ratio of 16:9. Many people are confused by the difference between 4:3 and 16:9, as at first glance they seem to be the same ratio. A simple math calculation will show you that 4:3 = 1.333, whereas 16:9 = 1.777. So it’s quite clear that the 16:9 ratio means a much wider screen! Most computer monitors are analogue display devices.

This means that although the computer produces digital signals, the monitor only accepts analogue signals. The monitor connects to the video adapter or graphics card inside the computer to receive analogue signals.

The Graphics Card

This is the device that converts a computer’s digital data output stream into analogue, so that the monitor can understand and display correctly. The graphics card receives digital data from the Central Processing Unit (CPU) and Random Access Memory (RAM) inside your computer, converts it all into an analogue signal and then sends the analogue signal to the monitor. This is what you finally see.

Most graphics cards also do advanced graphical computation and take away computing load from your CPU. These involve complex 3D computations that are required by most games of today.

How They Work Together

When you move your mouse, the mouse senses movement and sends the necessary data to the CPU, which in turn, makes sense of the movement and translates that into X (horizontal) and Y (vertical) coordinates. This data is sent to the graphics card or video adapter, which in turn, moves the mouse pointer that’s displayed on your screen to the correct co-ordinates. Since this all happens in millionths of a second, when you move your mouse, it appears to move smoothly across your screen, just as if there is a video playing. This is perhaps the most basic for of digital video that you see everyday on your computer!

It’s the same basic operation for everything you see on your computer, whether it’s moving a mouse, typing on the keyboard and seeing letters appear on your screen, or even watching a movie or playing a game. It’s all video, and all digital. If both monitor and graphics card support digital video inputs and outputs, respectively, you can have digital video all the way from the CPU to the monitor! Of course these are more expensive and rare, but are catching on fast.

Let’s move on to the real meat of Digital Entertainment, movies and movie clips that you watch, edit or shoot with the help of your computer!