Digital Video and Field Order 6/11/10 8:31 AM Copyright © 2002-2009 DVMP Miscellaneous Articles DVMP Pro Digital Video and Field Order Miscellaneous Links This article was written in 2002, so some of the details may be a little out of date. Contact There is a certain amount of confusion in the world of desktop video editing over “ Field Order”. Video newsgroups and bulletin boards attract a steady flow of queries about problems that people are experiencing with field order settings in their video projects. Much of this confusion is caused by conflicting terminology - “upper-field-first”, “ field order A”, “ field 1”, “odd field ” - and so on. Hardware and software manufacturers often give vague or $149 Only 4 Camera ambiguous advice on this subject, leaving many users with a feeling that they just don’t know what DVR is really going on, and why this should all be so complicated. Aowsome ! Call 1.888.688.9995 Now So I decided to get to the bottom of this. This involved going back to the standards for analogue High Quility video on which most digital video formats are derived and finding out how all of this confusion has &reasonable Price arisen, and the correct definitions for many of these contradictory terms. www.shoppingcctv.com/product The standards themselves make fairly dry reading, but there are some interesting details there Free Webex Remote which help to explain the roots of digital video. If we understand some of this then it all becomes a Support lot clearer. So, I’ve extracted some of these details and presented them in a series of simple Run diagnostics & diagrams which help to explain, for example, why certain resolutions are used and the concept of provide solutions in the notorious rectangular pixels used in the video world. real time - Try Free for 14 days The PAL television system runs at 25 frames a second. Each frame is comprised of 625 horizontal www.webex.com lines, and is made up of two interlaced fields separated in time by 1/50th of a second. If you number the lines from the top of the frame, the top line is 1 and the bottom line is 625. The first Cheap Video field contains the odd-numbered lines and the second field contains the even-numbered lines. But Surveillance you’ll probably know most of this already, so I’ll move on to the more interesting stuff. Lowest Prices, Widest Selection. Cameras, 4 Although in desktop video we are dealing with digital video, the roots of digital video are firmly and 8 Channel DVRs. planted in the original analogue video standards. Most readers in the UK will be interested in PAL www.gadspot.com which has 625 horizontal lines, but we will also be describing NTSC which has 525 lines. In fact it’s more accurate to refer to 625-line and 525-line systems rather than “PAL” and “NTSC”, so that is SAN for Pro Video what we will do in most of this article. We will start by describing the 625-line system because it Editing has fewer complications. Fibre Channel, 10Gb iSCSI and NAS – Up Analogue and Digital Active Areas to 64TB, 10 Users. TV/Film/Video OK, so let’s start with analogue video. “Interlaced” video is a continuous waveform comprising a www.StudioNetworkSolutions.com/Evo stream of fields which are “shot” at a rate of 50 fields per second. But each field only contains the Numara Remote alternate lines in the original picture. The first field “ field 1” contains the odd numbered lines Manager (assuming that you start counting from 1 rather than 0), and the second field “ field 2” contains Control Remote PC's. the even numbered lines 1/50th of a second later - we will refer to these fields as “F1” and “F2” for Silent Access. Secure. brevity. Encrypted. Easy to The analog waveform of a field carries a 'signature' that effectively identifies it as an F1 or F2 field Use. The signature occurs as a pattern of sync pulses that differs in F1 and F2 fields - this ensures www.NumaraSoftware.com that the lines of either field appear in the correct position on a television screen. When these two fields are interlaced you end up with all of the lines in the picture making a complete “Frame”. Zoom Q3 Video Each field has several lines which do not contain any picture information. These lines occur during Recorder the Vertical Blanking Interval (VBI) when the electron beam in the TV tube returns from the Record live bottom to the top of the screen. The VBI also covers several lines which carry data such as Closed performances with pro Captions and Teletext. quality audio and video. The lines which contain picture information comprise the “active” area of each field . The ITU-R www.discmakers.com/zoomQ3 BT.470-6 recommendation shows where the active picture area starts and ends in both fields . This is the analogue active area. Free Telepresence Systems ITU-R BT.601-5 and 656-4 describe a digital active area. This is used when the analogue video Enter to Win Two signal is converted to a digital format, and it does not exactly coincide with the analogue active file:///Volumes/GAMBIT/TO_ORG/Digital%20Video%20and%20Field%20Order.webarchive Page 1 of 12 Digital Video and Field Order 6/11/10 8:31 AM Polycom HD area. Conferencing Systems. $12K Value! The diagram below shows the analogue and digital active areas for a 625-line (PAL) system. www.Polycom.com/Telepresence CCTV Install & Repairs Commercial Cameras DVRs Monitors Call Today 800-397-5300 for a quote www.securityhunter.com Video Monitoring Systems Free Quotes - Multiple Dealers Find the Best Deal & Save! VideoMonitoring.BuyerZone.com Visit Solid Signal We Stock Digital Video Recorders Of Various Brands. Order Online! www.SolidSignal.com Video Monitoring Diagram 1 - 625-line Analogue and Digital Active Areas Systems Free Quotes - Multiple You can see how the two fields (F1 and F2) are interlaced together to make a frame. The frame- Dealers Find the Best based line numbers are shown on the left in black - these range from 1 to 625 from the top to the Deal & Save! bottom of a complete frame. VideoMonitoring.BuyerZone.com However, the ITU documents number the lines in temporal (i.e. chronological) order as they appear in the analogue waveform, so the lines of field 1 are numbered 1,2,3,4 and so on up to 313, and Visit Solid Signal the lines of the subsequent field 2 are numbered 314,315,316 up to 625. The numbers in brackets We Stock Digital show a different line numbering system used in some standards for field 2 which is 1 to 312. Video Recorders Of Various Brands. Order The solid lines show the analogue active area. Note that it starts and ends with a half-line. The Online! dotted lines show the Vertical Blanking Interval. www.SolidSignal.com The digital active area is shown between the two grey Digital Blanking areas. The digital active Download Video area starts with line 23 of field 1 and ends with line 623 of field 2 - that's 576 lines in total. The first half of line 23 and the second half of line 623 are part of the (analogue) VBI and do not Converter contain any picture data, but they are part of the digital active area all the same. AVI MPEG DVD WMV 3GP ASF FLV SWF RM Converting the analogue video waveform to digital involves sampling the analogue waveform at Fast And Easy Video regular intervals. ITU-R BT.601-5 states that both 525-line and 625-line systems are sampled at Converter the same rate of 13.5 MHz - that’s 13.5 million samples per second. This common sampling rate is www.avs4you.com/AVS-Video-Converterpartly to keep equipment costs down. Video Capture Now, interlaced PAL has 25 frames per second, each with 625 lines. So the number of samples on Software a single line must be: Capture, Edit, & Share Video Clips. 13500000 / 25 / 625 = 864 samples per line Download For Free Today! And for NTSC which has 29.97 frames per sec, each with 525 lines: www.JingProject.com 13500000 / 29.97 / 525 = 858 samples per line Roku® (Official Site) However, each line in the analogue video signal contains an area of horizontal blanking before and Roku Digital Player for after the picture data which is used to keep the TV display synchronised. And we have already Only $99! Watch explained that each field contains several complete lines of blanking (the VBI) before and after the 1000's of Movies on picture data. The sampling process is a continuous one which covers the whole video waveform Your TV. including the horizontal and vertical blanking regions, not just the actual picture area. So we can www.Roku.com represent a complete frame (of two interlaced fields ) as an area of samples 625 lines in height by 864 samples in width, and within this is the window which contains the actual picture - the digital active area. Cheap Video file:///Volumes/GAMBIT/TO_ORG/Digital%20Video%20and%20Field%20Order.webarchive Page 2 of 12 Digital Video and Field Order 6/11/10 8:31 AM Cheap Video The process of digitally capturing the analogue signal involves storing only the samples which Surveillance contain picture data - the samples from the horizontal and vertical blanking regions are usually Lowest Prices, Widest ignored. Selection. Cameras, 4 and 8 Channel DVRs. www.gadspot.com Video Capture Software Capture, Edit, & Share Video Clips.