VIDEO RECORDING TECHNOLOGY REFERENCE presented by Copyright Ó 2002 Peninsular Technologies. All rights reserved. TABLE OF CONTENTS DISCLAIMER..............................................................................................3 PREFACE...................................................................................................3 TAPE-BASED RECORDING FORMATS ............................................................4 VHS......................................................................................................4 S-VHS ..................................................................................................4 DIGITAL VIDEO (DV) FORMAT ................................................................5 NON-LINEAR VIDEO RECORDING.................................................................6 THE PERSONAL COMPUTER .....................................................................6 DIGITAL VIDEO ENCODING PARAMETERS .................................................6 FRAME RATE.......................................................................................7 RESOLUTION (FRAME SIZE)..................................................................7 BIT RATE............................................................................................8 MPEG VIDEO ........................................................................................9 MPEG-1.............................................................................................9 MPEG-2........................................................................................... 10 MPEG COMPRESSION........................................................................ 11 MPEG DECOMPRESSION.................................................................... 12 NON-LINEAR DIGITAL MEDIA................................................................ 13 DVD-R ............................................................................................ 14 RE-WRITABLE DVD .......................................................................... 15 CD-R............................................................................................... 16 HARD DRIVES.................................................................................... 18 TRADEMARKS.......................................................................................... 18 REFERENCES ........................................................................................... 20 Filename: Digital Video Technology Reference.doc v2.0 Printed on 5/7/02 3:08 PM CopyrightÓ 2002 Peninsular Technologies. All rights reserved. Page 2 of 20 DISCLAIMER This document is based on preliminary research conducted to answer frequently asked questions about video recording technology. Peninsular Technologies makes no warranty ensuring the accuracy of the information provided. Cost data was estimated based on retail offerings available at the time of authoring. PREFACE This document is intended to compare traditional tape-based recording systems to recently developed non-linear video recording systems. Video recording technologies are often presented in the context of a sewer inspection, but the information applies equally well to video recording applications in any industry. Filename: Digital Video Technology Reference.doc v2.0 Printed on 5/7/02 3:08 PM CopyrightÓ 2002 Peninsular Technologies. All rights reserved. Page 3 of 20 TAPE-BASED RECORDING FORMATS Linear magnetic tape has been a reliable video recording media for decades. Cassette sizes and styles evolved as the technology developed. Regardless of design, all cassette recorders save video information on a continuous line of magnetic tape. In order to retrieve a specific piece of information, the tape must be physically advanced or retracted until the point of interest is accessible by the reader head. The disadvantage of this characteristic grows as the size of a tape-based video library grows. VHS The venerable VHS tape preserves ~240 horizontal lines of resolution1. The majority of VHS VCRs cost $150 to $300. High-grade VHS tapes with 120 minutes of video recording time cost $1 to $2. The typical input/output connectors are composite RCA jacks. S-VHS Super-VHS (or S-VHS) technology is similar to VHS, but is capable of over 400 lines of horizontal resolution. Most S-VHS VCRs cost $300 to $800. S-VHS tapes that support the higher resolution cost $6 - $8 each, and hold 120 minutes of video at standard recording speed. S-VHS units include s-video connectors and cables, which preserve the high resolution video better than standard composite RCA cable. Regardless of the connector, all S-VHS VCRs record analog video. Filename: Digital Video Technology Reference.doc v2.0 Printed on 5/7/02 3:08 PM CopyrightÓ 2002 Peninsular Technologies. All rights reserved. Page 4 of 20 DIGITAL VIDEO (DV) FORMAT DV is an international video standard that is occasionally confused with the generic concept of “digital video” recording. Digital video broadly refers to the representation of a source signal with discreet reproducible digital packets, while DV is a small subset of this basic concept. Although the DV format is capable of high resolution recordings (~500 horizontal lines 2) with excellent video quality, the vast majority of DV recordings are saved on linear tape. This disadvantage results in a cumbersome linear navigation process on par with VHS or S-VHS tape. High-quality DV recordings can be transferred to non-linear media without signal degradation, but this approach requires extensive digital storage space. One minute of DV format video occupies approximately 270 megabytes of disk space, making non-linear DV archiving impractical for most consumers. The DV format has spawned several variations and sub-standards beyond the scope of this document. Links to additional information and retail products incorporating DV technology can be found in the References section.3 Filename: Digital Video Technology Reference.doc v2.0 Printed on 5/7/02 3:08 PM CopyrightÓ 2002 Peninsular Technologies. All rights reserved. Page 5 of 20 NON-LINEAR VIDEO RECORDING In a non-linear video system, images are recorded on non-linear or random access media. With random access digital media, individual video frames can be located directly, without having to advance or rewind a long magnetic tape. Furthermore, each video frame can be directly linked to supplemental information that describes the situation depicted by the frame. This supplemental information can be searched and sorted to quickly locate a specific video clip from a vast library of recordings. This video indexing technology is described in U.S. patent number 6,175,380 held by Peninsular Technologies and is currently available in the PipeTechÒ sewer TV inspection system. THE PERSONAL COMPUTER The PC is the cornerstone of mainstream non-linear video recording. In order to manipulate video with a computer, it must be digitized and recorded. This is achieved through a video capture device and a non-linear (random access) storage device. The hard drive in a PC is a non-linear device. CDs and DVDs are also examples of non-linear storage media and are discussed in more detail later in the document. In addition to digitizing a video signal, the PC is frequently used to compress the digital information for manageability purposes. Full-size, full- motion, uncompressed video is impractically large for today’s PCs. The application of a compression algorithm to a video signal in real-time is frequently called encoding. The inverse process of rendering a video stream from a compressed source file is called decoding. PCs can also use software to convert or compress existing video files in a transcoding process. DIGITAL VIDEO ENCODING PARAMETERS Digital video encoding can result in a wide variety of picture qualities, even more so than tape-based recording systems. Digital video encoding equipment typically specifies video quality in terms of three 3 variables: frame rate, resolution, and bit rate. Filename: Digital Video Technology Reference.doc v2.0 Printed on 5/7/02 3:08 PM CopyrightÓ 2002 Peninsular Technologies. All rights reserved. Page 6 of 20 FRAME RATE Frame rate is usually specified in frames per second (fps). The standard TV signal in North America is broadcast at 30 fps. The European equivalent standard specifies 25 frames per second. Motion pictures are typically filmed at 24 fps. At 15 fps, the human eye will clearly recognize a sequence of discreet images, and the illusion of continuous motion is lost. However, there are some benefits to low frame rate video. The corresponding file size is reduced in proportion to the reduction in frame rate. For example, any video clip digitized at 30 fps will be 3 times larger than the same clip digitized at 10 fps. If the appearance of the 10 fps video is acceptable, the smaller file size will be beneficial when storing, transporting, or broadcasting the video over a computer network. RESOLUTION (FRAME SIZE) In digital video terms, Source Input Format (SIF) resolution [352 x 240 pixels] is the closest approximation of VHS quality. Digital video frames can technically be any size, though most encoding devices only support a combination of the following choices at 30 fps. Resolution Name 175 x 120 (QSIF) 352 x 240 (SIF) 352 x 480 (Half D1) 640 x 480 (VGA) 704 x 480 (D1) 720 x 480 (D1 alternate) The frame size is an important factor determining the detail a video recording can preserve, but is only one of many variables that contribute to picture quality4.