Analog Video: Definition, Types, Standards, Applications and Current Status

What is Analog Video?

Analog video refers to video images composed of continuous analog signals. Most of the movies and TV programs we used to watch were based on analog signals. They are called "analog" because they simulate the physical quantities that represent sound and image information.
Cameras are the source of video signals. Early cameras used vacuum tubes as photoelectric conversion devices to convert external light signals into electrical signals. Different brightness levels of the object being shot in front of the camera correspond to different brightness values, which cause corresponding changes in the current in the camera's vacuum tubes. Analog signals use these current changes to represent or simulate the captured images, recording their optical characteristics. Through modulation and demodulation, the signals are then transmitted to the receiver, displayed on the fluorescent screen via an electron gun, and restored to the original optical images. This is the basic principle and process of TV broadcasting.
The waveform of an analog signal simulates changes in information, characterized by continuous amplitude (continuity means it can take infinitely many values within a certain range). Its signal waveform is also continuous in time, so it is also a continuous signal.
Advantages: Mature technology, low cost, and high system reliability. Disadvantages: Not suitable for long-term storage or multiple copies. Over time, the strength of image signals on video tapes will gradually attenuate, leading to problems such as image quality degradation and color distortion.

Types of Analog Video

Analog video signals mainly include luminance signals, chrominance signals, composite sync signals, and audio signals. To enable the transmission and connection of analog video in different environments, several signal types as shown in the figures are usually available:

1. Composite Video Signal: A single analog signal that contains luminance signals, color difference signals, and all timing signals. Its interface shape is shown in Figure (a). This type of video signal does not include audio signals and has a narrow bandwidth, generally providing only about 240 lines of horizontal resolution. Most video cards offer this type of video interface.

2. Component Video Signal: Each primary color component is treated as a separate TV signal. Each primary color can be represented by R, G, B, or by luminance-color difference, such as Y, I, Q or Y, U, V. Using component video signals is the best way to represent colors, but it requires a relatively wide bandwidth and sync signals. The VGA video signal output by computers is a component video signal, and its interface shape is shown in Figure (b).

3. Separated Video Signal (S-Video): A compromise between component video signals and composite video signals. It separates the luminance signal (Y) from the color difference signal (C), which not only reduces cross-interference between luminance and color difference signals but also improves the bandwidth of the luminance signal. Its specific interface shape is shown in Figure (c). Most video cards provide this type of video interface.

4. RF Signal: For long-distance transmission of analog video signals, it is necessary to modulate the full TV signal (including luminance, chrominance, composite sync, and audio signals) into an RF signal, with each signal occupying one channel. When a video receiving device (such as a TV) receives the RF signal, it first demodulates the full TV signal from it, then restores it to image and sound signals. The interface shape of the RF signal is shown in Figure (d), which is generally provided on TV cards.

Analog Video Standards

To facilitate the processing, transmission, and storage of analog video, relevant international analog video standards — broadcast video standards — have been developed to regulate and unify the analog video system. There are three main formats of analog video signals: PAL, NTSC, and SECAM.

1) PAL (Phase Alternating Line): A color coding method used in TV broadcasting. Proposed by German Walter Bruch while working for Telefunken in 1967, "PAL" refers to the TV standard with 625 scan lines, a frame rate of 25 fps, interlaced scanning, and PAL color coding. Except for parts of North America and East Asia that use the NTSC standard, and the Middle East, France, and Eastern Europe that adopt the SECAM standard, most regions in the world use the PAL standard.

2) NTSC (National Television System Committee): Also referred to as the N system, it is a color TV broadcasting standard developed by the U.S. National Television System Committee in December 1952. It belongs to the simultaneous system, with a frame rate of 30 fps, 525 scan lines, progressive scanning, and an aspect ratio of 4:3. The chrominance signal modulation of this standard includes both balanced modulation and quadrature modulation, which solves the compatibility problem of color and black-and-white TV broadcasting. However, it has the disadvantages of easy phase distortion and unstable colors. Most American countries such as the United States, Canada, and Mexico, as well as Taiwan, Japan, South Korea, the Philippines, etc., adopt this standard. Some TV companies in Hong Kong also broadcast using the NTSC standard.

3) SECAM (Séquentiel Couleur à Mémoire): Also known as the Secam system, which means "Sequential Color with Memory". Developed successfully in France in 1966, it belongs to the simultaneous-sequential system. During signal transmission, the luminance signal is transmitted line by line, while the two color difference signals are transmitted sequentially line by line. That is, the method of staggering the transmission time of lines is used to avoid color crosstalk caused by simultaneous transmission and the resulting color distortion. The SECAM standard is characterized by strong anti-interference ability and good color effect but poor compatibility. It has a frame rate of 25 fps, 625 scan lines, interlaced scanning, and an aspect ratio of 4:3. Countries adopting the SECAM standard mainly include Commonwealth of Independent States (CIS) countries (such as Russia), France, Egypt, and some French-speaking African countries.

Applications of Analog Video

Analog video once dominated many fields due to its mature technology and low cost:
In security monitoring, early analog cameras paired with coaxial cables and digital video recorders (DVRs) were widely used in communities, shopping malls, factories, and other places. They were favored for their simple installation and low cost, especially in small businesses and low-budget security projects.
In broadcasting and entertainment, analog TV broadcasts and video cassette recorders (VCRs) relied on analog video. For decades, people watched analog TV programs and recorded family gatherings or favorite shows on VHS tapes. Early camcorders also used analog signals to capture images.
In healthcare and industry, early medical equipment such as ultrasound machines and X-ray scanners used analog video to display images for doctors' observation. In factories, analog cameras monitored production lines in real time, helping workers detect faults promptly and ensure production safety.

Is Analog Video Outdated? Does It Still Have Uses?

It is true that analog video has been largely replaced by digital video in mainstream applications. Digital video offers clearer images, better anti-interference performance, easier storage and editing, and is widely used in modern devices such as HD TVs, IP cameras, and streaming services.
However, analog video is not completely obsolete. Many old security systems, especially in small businesses or rural areas, are still in operation because upgrading to digital systems is costly. In retro media circles, enthusiasts collect and use VCRs and analog camcorders to preserve old video tapes or enjoy vintage content. Additionally, some educational and repair workshops retain analog equipment to teach basic video technology principles.
In short, while analog video is no longer the mainstream, it still serves a purpose in specific scenarios, carrying the memory of visual media experiences for a generation.