Digital Video Broadcasting Technology

1. Basic Principles

Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion. Video technology was first developed for television systems, but has been further developed in many formats to allow for consumer video recording.

Starting in the late 70s to the early 80s, several types of video production equipment- such as time base correctors (TBC) and digital video effects (DVE) units (two of the latter being the Ampex ADO, and the NEC DVE)- were introduced that operated by taking a standard analog video input and digitizing it internally. This made it easier to either correct or enhance the video signal, as in the case of a TBC, or to manipulate and add effects to the video, in the case of a DVE unit. The digitized and processed video from these units would then be converted back to standard analog video.

Later on in the 1970s, manufacturers of professional video broadcast equipment, such as Bosch (through their Fernseh division), RCA, and Ampex developed prototype digital videotape recorders in their research and development labs. Bosch's machine used a modified 1" Type B transport, and recorded an early form of CCIR 601 digital video. None of these machines from these manufacturers were ever marketed commercially, however.

Digital video was first introduced commercially in 1986 with the Sony D-1 format, which recorded an uncompressed standard definition component video signal in digital form instead of the high-band analog forms that had been commonplace until then. Due to the expense, D-1 was used primarily by large television networks. It would eventually be replaced by cheaper systems using compressed data, most notably Sony's Digital Betacam, still heavily used as a field recording format by professional television producers.

Consumer digital video first appeared in the form of QuickTime, Apple Computer's architecture for time-based and streaming data formats, which appeared in crude form around 1990. Initial consumer-level content creation tools were crude, requiring an analog video source to be digitized to a computer-readable format. While low-quality at first, consumer digital video increased rapidly in quality, first with the introduction of playback standards such as MPEG-1 and MPEG-2 (adopted for use in television transmission and DVD media), and then the introduction of the DV tape format allowing recording direct to digital data and simplifying the editing process, allowing non-linear editing systems to be deployed wholly on desktop computers.

As a consequence of the digital era, attempts to display media on computers where made that date back to the earliest days of computing, in the mid-20th century. However, little progress was made for several decades, due primarily to the high cost and limited capabilities of computer hardware.

Academic experiments in the 1970s proved out the basic concepts and feasibility of streaming media on computers. While during the late 1980s, consumer-grade computers became powerful enough to display various media. The primary technical issues with streaming were:

• having enough CPU power and bus bandwidth to support the required data rates

• creating low-latency interrupt paths in the OS to prevent buffer under-run

However, computer networks were still limited, and media was usually delivered over non-streaming channels, such as CD-ROMs.

Eventually in the 1990s the technology erupted bringing along:

• greater network bandwidth, especially in the last mile

• increased access to networks, especially the Internet

• use of standard protocols and formats, such as TCP/IP, HTTP, and HTML

• commercialization of the Internet

These advances in computer networking, combined with powerful home computers and modern operating systems, made streaming media practical and affordable for ordinary consumers. Stand-alone Internet radio devices are offering listeners a "no-computer" option for listening to audio streams.

In the following pages we will describe one of the most widely accepted methods, that is being used nowadays to broadcast digital video to millions of viewers; Flash Video.

2. Digital Video Broadcasting Technologies

There are numerous video broadcasting (streaming) technologies available nowadays which are briefly described in the following section:

2.1