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Video and Audio Transport Technologies

In this article we explore the many technology standards used for transporting video and audio, and some details about applicable Matrix Switch Corporation products.

Overview

Media transport standards can be divided into two main categories: analog and digital. Advances in digital circuitry have led to the dominance of digital media standards over its analog predecessor, because of the inherent resilience to distortion and signal degradation which analog standards suffer from. Analog solutions are still frequently employed though, for interfacing to legacy infrastructure or equipment, and also for its simplicity and potential cost savings in some applications.

Video Properties

Video is usually defined by several properties, including: Frame Size (width and height in pixels), Frames Per Second (FPS), and Interlaced or Progressive scan types.

The relative difference between the width and height of a frame is called the Aspect Ratio and is usually calculated by dividing the width by the height and is often written as a relative ratio W:H. For example, the standard VGA frame size is 640 pixels wide by 480 pixels high which is 640/480, but is usually written as a 4:3 aspect ratio (fraction) or ~1.33. Larger VGA frame sizes such as 1024x768 have the same 4:3 aspect ratio. The popularity of wide screen aspect ratios has been largely driven by cinematic productions and has influenced both television and computer screens. The most popular aspect ratio is now 16:9.

Frame sizes are often referenced by the number of lines (height) of the frame followed by a p for progressive or i for interlaced. Progressive scan means that each video frame contains every line of the video picture. Interlaced formats usually provide half of the lines for each frame, alternating between even and odd lines. Interlaced formats were originally employed with broadcast television to perceptively provide double the frame rate, without increasing the required bandwidth. Thus improving the perception of motion and reducing flicker, by sacrificing vertical resolution per frame. Modern LCD screens are inherently progressive and run at higher frame rates than legacy televisions, leading to progressive video now being the dominant scan type. Popular video formats include: 720p, 1080p, 2160p, and 4320p. These are all 16:9 wide screen progressive formats with frame sizes of 1280x720, 1920x1080, 3840x2160, and 7680x4320 respectively.

The number of Frames Per Second determines the perceived fluidity of motion and how fast a frame changes from one to the next. This is often abbreviated as fps or just as a number following the p or i when specifying the format as the number of lines. For example 1080p30 is a progressive frame size of 1920x1080 at 30 frames per second. Typical frame rates include 24, 25, 30, 50, 60, 29.97, and 59.94. The last two non-integer frame rates are related to legacy NTSC broadcast television formats and were chosen for convenience due to technological limitations of the time.

There are several Color Models used for encoding the color, brightness, and contrast information of a picture. The two most common ones are YUV and RGB. YUV consists of 3 components one luminance (brightness) component Y and two chrominance (color) components U and V. It was chosen in the early days of color television in order to provide backwards compatibility with black and white TV broadcasts and televisions, since color broadcasts were chosen to consist of the existing black and white Y signal, with additional U and V components, which when absent simply resulted in a black and white image. YUV has continued to be used in digital video technologies and it tends to be more conducive to digital compression. RGB encodes images as Red, Green, and Blue components, which are the primary additive colors, which is what YUV signals are ultimately converted to when displaying on a CRT or LCD screen, because of the additive nature inherent in mixing emitted light to make the wide spectrum of visible colors. With RGB, each channel consists of color and brightness information for each of the primary colors.

Several more important parameters are specific to certain standards and are described in further sections below.

SDI Digital Video & Audio

SDI (Serial Digital Interface) has become a dominant standard in the broadcast industry. It is an uncompressed digital video and audio standard which was first defined in 1989 with specifications for broadcast quality video commonly referred to as SD-SDI (Standard Definition), followed later by ED-SDI, HD-SDI, 3G-SDI, 6G-SDI, and 12G-SDI each offering higher digital bit rates, resulting in increased video resolutions/frame rate capabilities.

Each standard bit rate defines a set of supported video formats. SD-SDI supports 480i and 576i formats. ED-SDI defined progressive frame formats for broadcast quality video at a bit rate of 540 Mbit/sec. HD-SDI operates at 1.485 Gbit/sec (1.5G) and defines a maximum of 720p60 and 1080i30 video formats. 3G-SDI runs at 2.97 Gbit/sec and offers up to 1080p60. 6G-SDI has a bit rate of 5.94 Gbit/sec and up to 1080p120 and 2160p30. 12G-SDI has a rate of 11.88 Gbit/sec and 2160p60 video.

Additional parameters relate to what color model is used and how the components are stored. For example 10 bit 4:2:2 YCbCr is the most common and stores each sample as a 10 bit number with the Y component having the same bandwidth as the Cb and Cr components combined (U and V equivalents in analog video).

SDI also supports embedded audio with up to 16 channels for SD-SDI and HD-SDI formats and 32 channels for 3G-SDI formats. Typically this is PCM encoded audio with a sample rate of 48 KHz and 24 bit sample words, encoded as AES compatible data. See AES Digital Audio section below for more details.

Physical connectors and cabling for SDI consists of coax cable and BNC or HD-BNC connectors. All Matrix Switch Corporation SDI products utilize full size BNC connectors.

Matrix Switch Corporation provides a very wide selection of Fixed Size SDI Routers, Modular SDI Routers, SFP SDI Converters, and SDI Distribution Amplifiers. Our standard routers provide 3G-SDI support and we also offer a selection of 12G-SDI Routers.

HDMI Video & Audio

HDMI (High-Definition Media Interface) provides a digital video and audio interface standard which is often used for monitors, projectors, and other display devices. There are several versions of this standard, each providing additional features. Version 1.0 provided a max bit rate of 3.96 Gbit/sec data rate and support for up to 1080p60 and 8 channels of 192 KHz 24 bit audio. Version 1.2 introduced several more formats and improved use with PC computers among many additional notable features. Version 1.3 increased the usable data bit rate to 8.16 Gbit/sec for up to 2160p30. Version 1.4 added several additional formats, a 100 Mbit/sec Ethernet interface, an audio return channel, 3D formats, and several additional features. Version 2.0 increased usable bandwidth to 14.4 Gbit/sec supporting up to 2160p60 and 2880p30. Version 2.1 was released in 2017 and increases data bandwidth to 42.6 Gbit/sec, supporting 4320p30 (8K) and many higher bandwidth formats with Display Stream Compression (DSC).

Matrix Switch Corporation Modular SDI Routers, such as the MSC-XDM1000L, MSC-XDM2000L, and MSC-XDM4000 support HDMI with Modular SFP SDI Cards and HDMI SFP Receiver and HDMI SFP Transmitter modules.

Analog Video

Some additional properties of Analog Video are the bandwidth required to transport the signal, usually specified in MHz - defining the maximum analog frequency passed with acceptable levels of distortion and whether the video is Composite or Component. Composite analog video signals consist of a single signal, in contrast to component which separates out individual channels of the video stream. Such as splitting the individual Y, U, and V components or R, G, and B components of the YUV or RGB color models into separate signals.

Matrix Switch Corporation analog video products include several sizes of Composite Analog Routers, including: 16x16, 16x64, 32x32, 32x48, 48x32, and 64x16. We also offer a range of VGA Analog Video Routers.

AES3 Digital Audio

Digital audio introduces a few more properties compared to analog audio which relate to converting audio to and from digital. The Sample Rate refers to the number of samples (measurements) which are made per second of the audio signal amplitude and is usually measured in Hz or KHz. For example a sample rate of 48KHz would mean 48,000 samples per second. The Bit Width of a digital audio signal indicates how many digital bits are utilized to store the amplitude value of each audio sample. For example, 24 bit digital audio utilizes 24 bits for storing the amplitude, which can store 2^24 (~16 million) values.

AES3 Digital Audio is typically 24 bit, but supports bit widths from 16 to 24 and sample rates up to 192 KHz.

AES3 utilizes a number of different connectors and cabling, including balanced XLR, unbalanced RCA, optical fiber, and AES-3id 75 Ohm BNC and coax. Matrix Switch Corporation products utilize either AES-3id 75 Ohm BNC connectors or DB25 female connectors supporting up to 8 balanced AES-3id 75 Ohm connections.

We offer several AES digital audio products, including several sizes of AES Audio Routers (standalone and companion router levels). We also offer compact 1RU SDI routers with AES Audio Support as a built-in additional routing matrix level.

Analog Audio

The most important properties of analog audio systems are Frequency Response and Signal-To-Noise Ratio, which are all indicative of how well the analog signal is reproduced from its original form and conversely how much distortion is introduced.

Frequency Response is usually defined by a frequency range within which frequencies are passed with acceptable amplification levels. For example 20 Hz to 20 KHz is typically referenced as human hearing range, though most individuals will have a much narrower range of hearing than this, especially with higher frequencies. More accurate representation of frequency response will show a graph of amplification gain based on the frequency of the input signal, called a frequency response curve.

Signal to noise (SNR) ratio is the difference of the power output of the original signal to the power of unwanted distortion added by a piece of equipment. It is usually specified in decibels (dB) and typically measured with a 1 KHz sine wave input signal at +4 dBu. Generally the higher the SNR ratio is the better. For example, a SNR of 100dB would indicate that the output is 100dB greater in magnitude to unwanted noise or in other words the signal would be 20 X the amplitude of the noise.

We offer several Analog Audio Routers as standalone or companion router levels. Our routers use DB25 connectors which offers up to 8 balanced analog audio channels per connector using a Tascam compatible pinout, providing the ability to use several 3rd party breakout cables.