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HDV Progressive Primer
Table of contents Introduction ...... 3
• What is HD? ...... 4
• What is HDV? ...... 5
• Progressive Shooting in HDV Format ...... 6
• Interlace and Progressive Scanning ...... 6
• Progressive Programme Distribution ...... 8 Interlace and Progressive Imagers ...... 9 Interlace and Progressive Recording ...... 9
• Progressive Shooting Functions in Sony’s Professional HDV Camcorders ...... 10
CineframeTM (HVR-A1, HVR-Z1) ...... 10 Progressive Scan Mode (HVR-V1, HVR-Z5, HVR-Z7, HVR-S270) ...... 11 Native Progressive Recording Mode (HVR-Z5, HVR-Z7, HVR-S270) ...... 12
• Edit and Distribute the Video Taken in Progressive Shooting Functions ...... 13 For Video Distribution in an Interlace Format with Progressive-look Motion ...... 13 For Video Distribution in a Progressive Format ...... 13
Appendix • 50i/60i Switchable Option of HVR-Z5, HVR-Z7 and HVR-S270: ...... 15
• Why 29.97 and 23.98 fps, not 30 and 24 fps? ...... 15
• 24p to 60i Transfer – 2:3 pull-down – ...... 16
• 24P Scan Modes in HVR-V1/Z5/Z7/S270 – “24” or “24A” ? – ...... 17
• HDV Native Progressive Recording format ...... 18 An Optional Specification in HDV Format ...... 18 Compression Structure ...... 18 Output Signal (in HVR-Z5/Z7/S270/M15A/M25A/M35) ...... 19 Recorded and Output TimeCode (in HVR-Z5/Z7/S270/M15A/M25A/M35) ...... 19
• HDV Compression ...... 18 The Concept of Entropy and Redundancy ...... 20 Inter-frame Coding ...... 22 Intra-frame Compression ...... 22 Building an HDV Stream ...... 23
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HDV Progressive Primer
Welcome to this Sony HDV TM Progressive Primer designed to explain the art and craft of shooting progressive, the technology behind progressive video, and show you the controls, functions and benefits of the latest range of Sony HDV progressive products.
The Purpose of This Primer HDV, and high definition video, push the boundaries of quality and artistic expression. Camera operators can be more adventurous, and editors have a greater range of techniques to play with. Now, the latest Sony HDV camcorders bring the ability to shoot in the HDV native progressive recording format. While this new capability opens the envelope of opportunities to those using these camcorders, progressive also brings with it several new technologies. Technologies that have been used very little in standard definition programme making. Although Sony HDV progressive products will record a perfectly good image with little or no effort, anyone wanting to gain the most from these products should understand the new controls, functions and technologies behind progressive. This primer tells the story behind progressive video. It provides a technical explanation of the progressive shooting capabilities of the Sony range of professional HDV camcorders, referring to both the operation of the camcorderÅfs image sensors and the video signals they produce. By using this primer and Sony HDV progressive products, you will find the best combination of controls and functions, for a wider range of shooting conditions, and a greater variety of final video clips, allowing you to shoot a superb image and build a well crafted edit. Progressive recording will become part of your overall programme making process, and another expressive technique to add to those you already have.
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◆◆◆ What is HD? Standard Definition (SD) video has been available in two versions with 525 lines and 625 lines per video frame. Europe, Australia, India and some other countries have adopted the 625 line version commonly referred to as PAL. The USA, Canada and some other countries have adopted the 525 line version commonly referred to as NTSC. (A third standard, SECAM, was devised as an alternative to PAL, and is used by France, Russia and some other countries for transmitting television into the home. However, because of its relative complexity, but close similarity to PAL, all countries that use SECAM to transmit to the home use PAL for original recording and in the television studio.) The term “High Definition” has been used throughout the history of television to mean the next and best television format. For example, in the 1930s monochrome analogue television broadcasting began in Europe at only 405 lines per frame. At the time this was also called “High Definition” simply because it was better than previous television of the time! With modern television High Definition (HD) has come to mean anything significantly better than 625 line television, and probably approaching 1000 lines per frame. HD is now available in two types with 720 and 1080 lines per video frame. Both are significantly better than existing SD television formats offering better movement capture and higher resolution.
176 352 720 1280 1920
OCF 176x144 144 CIF 352x288 288
SD (DV) 720x480, 720x576 480 or 576
720 (HD) 1280x720 720
1080 (HD) 1920x1080 1080
Chart illustrating the relative pixel resolution of different video formats.
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Srandard Definition High Definition (1920x1080) both images are made the same height. Comparing SD with 1080 HD. In comparison
Comparing standard definition and high definition There are about 5 times as many 1080 HD pixels as SD television.
◆◆◆ What is HDV? DV and its professional brother DVCAMTM have enjoyed huge success as a cost effective compact SD format, and many users, both non-professional and professional, have adopted both DV and DVCAM as their entry level programme making formats. Now HDV maintains the heritage into the exciting new world of HD video. HDV is a tape recording format using DV tape to record HD video, thus providing all the quality and resolution benefits of HD but using equipment that is compact and easy to operate, with media that is both easy to obtain and cost effective. In a nutshell, HDV is the entry level HD format for broadcasters, videographers and programme makers alike. Both 720 and 1080 high definition types are supported by HDV. The 720 lines HDV type uses progressive scanning and is generally called HDV720p. The 1080 line HDV type traditionally uses interlaced scanning and is generally called HDV1080i. Initially Sony adopted HDV1080i for its HDV products. Recently, the HDV specification was widened to include native 1080P recording capability. The HDV1080 features 1080 lines and 1440 pixels per line. HDV compresses the full HD image, by using one of the MPEG-2 Long GOP profiles, Main Profile at High 1440 Level (MP@H-14). This highly efficient and robust MPEG-2 Long GOP codec is also used in the Sony XDCAM HD and XDCAM EX series of professional products and enables users to record stunning-quality HD video. For more details of HDV compression, please refer to the Appendix at the end of this Primer.
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Sony has adopted HDV1080i for all its HDV products.
◆◆◆ Progressive Shooting in HDV Format Traditionally HD progressive shooting was reserved for the 720 line HD specification. More recently, 1080 progressive capabilities have also been adopted in the many types of HD camcorders. The Sony HDV camcorders are no exception. Sony professional HDV camcorders have several types of progressive shooting functions. The HVR-Z1 and HVR-A1 have “CineframeTM” progressive-look mode , the HVR-V1 has the “Progressive Scan” mode and the latest HVR-Z5/Z7/S270 have the additional “Native Progressive Recording” mode. When a suitable mode is selected, programme makers can enjoy all the benefits of shooting in progressive.
◆◆◆ Interlace and Progressive Scanning Video portrays a moving scene as a series of images displayed at such a fast rate that we perceive a moving picture. Each of these images is called a frame (a term borrowed from film). The chosen frame rate for SD video is 25 frames per second for 625 line areas, and 30 frames per second for 525 line areas. These rates were originally chosen to match AC mains power supplies in countries around the world, and to reduce the objectionable beating effects that would otherwise occur when televisions and room lighting interfere with one another. However, at 25 or 30 frames per second television image tends to flicker. To reduce flicker without increasing the required bandwidth for the television signal, each video frame is divided into two scans called fields, with field 1 for the odd lines and field 2 for the even lines. The screen is therefore scanned at 50 and 60 fields a second respectively, reducing flicker, and each frame is made up from two fields. This technique is called interlaced raster scan or simply interlace.
Movement looks smoother with interlace thanks to its relatively high field-rate. However, interlace may give jagged edges on moving objects when viewing a single frame on its own, commonly referred to as jaggies. This is because the position of the object has moved from field 1 to 2. Jaggies are undesirable in some applications such as image composition, viewing on computer screen, film transfer, etc..
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1/25 or 1/30 sec.
1/50 or 1/60 sec.
Scan lines
Fly-back Field 1 Field 2 (blanking)
Interlace scanning
Object An object moving from left to right quickly
Interlace scanning
Field 1 (Odd field) Time Field 2 (Odd field) Difference Jaggies 1/50 sec. or 1/60 sec.
Frame
Jaggies appear on the edge
Jaggies
In these cases the “filmic” look is often a better alternative over interlace, where each video frame is kept as a single scan. This is called progressive raster scan or simply progressive. With progressive, jaggies do not occur. This makes it much better than interlace if you plan to capture still images from your video. It also gives the video a characteristic filmic look.
1/25 or 1/30 sec.
Scan lines
Fly-back (blanking) Frame
Progressive scanning
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◆◆◆ Progressive Programme Distribution The following are examples of progressive programme distribution:
Film: For film-making with video camcorders, it is necessary to print film for final distribution. Progressive shooting is ideal for film-out because each frame is captured at once, just as a film camera would and at the same frame rate as film.
Web movie and computer graphics: A computer display uses progressive scanning. It is ideal to make a video in progressive format for viewing on this type of display.
24P on Blu-ray DiscTM DVD and Blu-ray Disc are capable of storing native 24P content. Most Hollywood movies are recorded on the disc as a 24P (23.976p) stream. 24P-capable DVD and Blu-ray Disc players can deliver the 24P signal to a computer monitor or a 24P-capable TV set at 24 fps with no 2:3 pull-down just as it would appear in a movie theatre.
For 25P users, it is possible to convert the 25P to 24P and vice versa by copying frames one on one. There is a difference of only one frame per second. It is equivalent to a 4% speed difference. Some NLE software or digital motion graphics software have a frame rate conversion function.
25P 24P
1 1
2 2 1 sec.
1 sec. • • • • • •
24 24
25 1
1 2
Conversion between 25P and 24P
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Interlace and Progressive Imagers Camcorders can adopt image sensors that capture video frames using either interlace or progressive scans. For true interlace recording the imager should scan in an interlace pattern, and for true progressive recording the imager should scan in a progressive pattern.
Interlace and Progressive Recording Camcorders can record to media using either an interlace method or a progressive method. When using progressive recording the video frame is recorded to media as one block of data. When using interlace recording the video frame is recorded in two blocks, one for the odd lines and the other for the even lines.
Recording Interlace Progressive
[HVR-A1 & HVR-Z1] Not used in Sony HDV True interlace recording with equipment. May be used in the imager and recording HDV equipment from other Interlace system matched. Used in 1080i manufacturers. Could result in mode. degraded image quality due to lack of scanning lines.
[HVR-V1, HVR-Z5, HVR-Z7, HVR-S270] (1): Interlace scanning A Progressive imager can work as an interlace imager. In interlace recording mode, Imager true interlace recording is realized. [HVR-Z5, HVR-Z7, HVR-S270] (2):Progressive scanning True progressive recording Progressive Progressive segmented Frame with the imager and recording (PsF) recording. True system matched. progressive capture. Frame Used in HVR-Z7 and HVR-S270 split into two segments and as “Native Progressive recorded using the same Recording” mode. technique as interlace recording. PsF is a progressive signal that can be displayed on an interlace-only monitor. Used in “Progressive Scan” mode.
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◆◆◆ Progressive Shooting Functions in Sony’s Professional HDV Camcorders The Sony range of professional camcorders has several types of progressive shooting functions.
CineframeTM (HVR-A1, HVR-Z1) Cineframe gives a progressive-look motion to the video captured by the interlace imager, which is then processed and recorded as a normal interlace signal. As described previously, each interlace frame is composed of two fields. In Cineframe mode, one field is ignored and another field is duplicated to make a complete video frame free from jaggies. Although each frame has half the resolution (540 lines), the recorded video can be conveniently viewed and edited by normal interlace facilities. The Cineframe method is a useful way of recording a filmic look on a camcorder that uses interlace imagers. However this method falls short of the true quality attainable by a camcorder fitted with progressive imagers that can record true native progressive.
Cineframe is also available in DVCAM and DV recording modes.
For 60i model: 60i models of the HVR-Z1 and HVR-A1 include the Cineframe24 mode, which uses 2:3 pull-down to synchronize the frame/field frequency. For more detail about the 2:3 pull-down method, please refer to the Appendix in this Primer.
Field1 (odd field)
3. Progressive-look motion 1. Extact one field by these two fields
2. Duplicate to another field
Field2 (even field) Cineframe
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Progressive Scan Mode (HVR-V1, HVR-Z5, HVR-Z7, HVR-S270) The HVR-V1, HVR-Z5, HVR-Z7 and HVR-S270 camcorders all use 3 ClearVid CMOS SensorTM system which can capture 1080p full-HD quality video. These models have Progressive Scan mode. In this mode, the captured 1080p image is just divided into two halves, then recorded or output as interlace signal. The halves are called segments, not fields, because there is no temporal difference between them. This method is also called as PsF (Progressive segmented Frame) recording. The 1080p picture quality is completely kept unlike the Cineframe so that you can use this mode instead of the Cineframe.
The Progressive Scan mode is suitable for the feature films, documentaries, music videos which have to be recorded as interlaced video for viewing on interlaced monitors, but want to offer “progressive-look” to their motion.
Besides, the video taken in the Progressive Scan mode can be edited and output as true progressive video if needed. For 25p or 30p scan, most NLE can output the edited timeline in progressive format by merging the divided odd and even fields again.
For 60i model: For 24p scan of the 60i models , the image is recorded through the 2-3 pull-down process. You can use your current interlace-based editing system because the recording is done in interlace. For more detail about the 24p scan mode, please also refer to the Appendix in this Primer.
Capture Record Edit Deliver 1080p 1080i 1080p or 1080i 1080p or 1080i
Odd Field
1080p 1080p
Even Field
1080i 1080i Progressive-look Motion
Progressive Scan mode
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Native Progressive Recording Mode (HVR-Z5, HVR-Z7, HVR-S270) The HVR-Z5, HVR-Z7 and HVR-S270 can record the captured 1080p image as HDV native 1080 progressive signal which is defined as an optional format of HDV1080i specification. (Please refer to : http://www.hdv-info.org/).
In this mode, the captured 1080p image is recorded on the media without any conversion. A compatible NLE can directly capture the HDV1080/24p/25p/30p i.LINK output stream and edit it natively.
The picture quality of Native Progressive Recording mode is theoretically better than Progressive Scan mode. In practice it is difficult to determine the difference in most video sequences. Please refer to the flow chart in this Primer to know the better mode for you.
Native Progressive Recording has been called 24F/25F/30F in some camcorders, while actually using interlace CCD imagers. However the Sony HVR-Z5, HVR-Z7 and S270 have true 1080p CMOS imagers, and true progressive processing. The compatible Sony’s HDV products have the following logo :
Capture Record Edit Deliver 1080p 1080p 1080p 1080p
HDV Native Progressive Recording mode.
For more information about the HDV Native Progressive Recording format, please refer to the Appendix of this Primer.
Camcorder models and progressive shooting functions
Progressive Native Model Imager Cineframe scan mode progressive recording mode 1/3-type 3 ClearVid HVR-S270 CMOS Sensor system NO YES YES 1/3-type 3 ClearVid HVR-Z7 NO YES YES CMOS Sensor system 1/3-type 3 ClearVid HVR-Z5 NO YES YES CMOS Sensor system HVR-Z1 1/3-type HD 3CCD YES NO NO 1/4-type 3 ClearVid HVR-V1 YES CMOS Sensor system NO NO HVR-A1 1/3-type single CMOS YES NO NO 1/2.9-type single HVR-HD1000 NO NO NO ClearVid CMOS Sensor
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◆◆◆ Edit and Distribute the Video Taken in Progressive Shooting Functions
For Video Distribution in an Interlace Format with Progressive-look Motion If you decide to deliver your programme in an interlace format only, you should record material in Cineframe or Progressive Scan mode. Material is recorded in an interlace fashion, but has a progressive look, and can be edited as an interlace (60i or 50i) project on standard NLE software. The result can be authored to Blu-ray Disc, DVD, tape etc. as an interlaced video for viewing on a television with a progressive or “filmic” look.
For 60i model users: If you just need a progressive-look image for viewing on a television screen, please consider shooting 30P scan. 30P scanned images look more natural than 24P.
For Video Distribution in a Progressive Format You can distribute video shot in a progressive mode as, for example, progressive Blu-ray Disc, film, web movie or any other progressive format media. There are several options for this case.
1. Video shot in Native Progressive Recording mode (HVR-Z5, HVR-Z7 and HVR-S270) If you have an NLE software compatible with this format, it is recommended to shoot footage in this mode. The NLE can capture the HDV native progressive signal through the i.LINK cable and you can edit the material as a 23.98p/25p/29.97p project.
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2. Video shot in Cineframe or Progressive Scan mode If your NLE software does not support native progressive editing, but your goal is a 25p or 30p programme, you can use “Cineframe25/30” or “Progressive Scan 25p/30p” mode. Capture the material in either of these modes, and edit as an 50i/60i project. Output the finished timeline as a progressive format by selecting the suitable output settings in the NLE. Most NLEs can merge the odd and even fields to make one frame during output.
For 60i model users: If you would like to make 24p programme, you have to have NLE software compatible with 24A Progressive Scan mode. The 24A compatible NLE can detect 2-3 cadences and remove them in order to edit in 23.98p. For the detail about the 24A Progressive Scan mode, please also refer to the Appendix of this Primer.
The following flow chart explains the recommended progressive shooting functions.
Find your best progressive function •Progressive Scan 25/30 •Cineframe 25/30 25p/30p Converted to progressive by NLE
25p/30p or 24p ? •Progressive Scan 24 No •Cineframe 24 Use software with Do you have any No 24p Do you have a 24A inverse telecine function*1 NLE compatible with compatible NLE ? the native progressive format ? Yes Yes Progressive Scan 24A NLE removes 2-3 frames Only Progressive •Native 24P/25P/30P
What format Only Interlace •Cineframe 24/25/30 for the final •Progressive Scan 24/25/30 distribution ? •Progressive Scan 24 •Cineframe 24 •Progressive Scan 25/30 Interlace: Edited in 60i •Cineframe 25/30 Both or Progressive: Use software Interace: Edited in 50i/60i Not decided with inverse telecine 25p/30p Progressive: Converted to function*1 progressive by NLE No 25p/30p or 24p ? •Native 24P Do you have any NLE Interlace: compatible with the NLE inserts 2-3 frames*2 No native progressive Progressive: Yes 24p format ? Edited in native Progressive Do you have a 24A compatible NLE ? •Progressive Scan 24A Interlace: Yes Edited in 60i Progressive: NLE removes 2-3 frames
*1: Some application software such as Adobe After Effects®, Apple® Cinema ToolsTM, Cineform Aspect HDTM can remove the 2-3 frames from “24” scan video materials by their inverse telecine function. For more details, please ask the reseller of these software. *2: NLE needs to insert the 2-3 pull-down frames to the 24p data.
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Appendix
◆◆◆ 50i/60i Switchable Option of HVR-Z5, HVR-Z7 and HVR-S270: 50i/60i switchable function is added on the HVR-Z5/Z7/S270 when modified at an authorized Sony service centre. The following recording modes are added: HDV1080i recording: • 60i, 24p and 30p modes on 50i model • 50i and 25p modes on 60i model DVCAM/DV recording: • 60i mode on 50i model • 50i mode on 60i model Please consult your local Sony service centre for the fee and details.
◆◆◆ Why 29.97 and 23.98 fps, not 30 and 24 fps? NTSC video equipment brochures and manuals often mention 29.97 or 59.94 fps rather than 30 or 60 fps. Why? Original monochrome NTSC video, set in 1941, ran at 30 frames per second, interlaced at 60 fields per second. This standard worked well and many American television stations adopted the standard, and thousands of viewers at home bought televisions to receive monochrome NTSC. However when the NTSC colour standard was designed it was found that the additional colour signal interfered with audio when the signal was transmitted out to the home. The standards authorities therefore decided to alter the video frame rate slightly from 30 frames per second to 29.97 frames per second, removing the interference. This is sometimes called drop-frame because timecode needs to drop a few frames every so often to ensure that its count is kept in line with real time. Thus drop frame NTSC runs at 29.97 frames per second, or 59.95 fields per second. Many American broadcasters shoot at film frame rate, 24 frames per second. Therefore a TV version of 24 frames per second was also devised at 23.98 (23.976) frames per second. These frame rates are used to this day, even in high definition video and all Sony HDV equipment actually operates at 29.97 frames per second when 30 frames per second is selected, and at 23.98 frames per second when 24 frames per second is selected. In this primer, 30p, 60i and 24p actually mean 29.97p, 59.94i and 23.98p respectively unless otherwise specified.
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◆◆◆ 24p to 60i Transfer – 2:3 pull-down – Film is recorded at 24 complete frames per second. This frame rate was chosen for historic reasons because it is about the slowest frame rate possible before filmic judder becomes unacceptable, using a little film stock as possible, as film was expensive, certainly in the early day of cinema. Cinemas, however, show film at 48 frames per second by displaying each frame twice. While this does not alter filmic judder because movement is still running at 24 images per second, it does make the picture appear smoother by improving flicker In 60Hz regions, film transfers must be converted from 24 frames per second to 60 fields per second interlace for TV broadcast by repeating some fields. The process is known as 2:3 pull-down (sometimes also called as 3:2 pull-down). This process is also used in camcorders which have 24p scanning capability. The first 24P frame is used to make the first two 60i fields (first complete 60i frame). The second 24P frame is used to make the next three 60i fields, that is the second complete 60i frame and the first field of the third 60i frame. The third 24P frame is used to make the next 2 fields, that is the second field of the third 60i frame and the first field of the forth 60i frame. The forth 24P frame is used to make the next three fields, that is the second field of the forth 60i frame and both fields of the fifth 60i frame. Thus every four 24P frames make ten 60i video fields. 2:3 pull-down repeats this process again and again to transfer from 24 frames per second to 60 interlace video fields per second. 2:3 pull-down builds some strange looking video frames with fields taken from two film frames. Editors need to recognise the 2:3 pull-down sequence to avoid these frame, especially in edits that will be transferred back to 24P in the future.
Original Odd Field Even Field Resulting 24 Frames (60i) (60i) Video Frame
2:3 pull-down method
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◆◆◆ 24P Scan Modes in HVR-V1/Z5/Z7/S270 – “24” or “24A” ? – The HVR-V1/Z5/Z7/S270 have the Progressive Scan modes. In these modes, the captured 1080p image is just divided into two halves, then recorded or output as interlace signal. For the 24P Scan modes, the 2:3 pull-down method is used. It is possible to edit the 24P scanned images as 23.98p by using compatible NLE software. The NLE software can remove the 2:3 pull-down frames. For 24P scan, please note that there are two options in the menu. One is “24” setting and another is “24A”. In non HDV camcorders, 24A means “advanced” pull-down with a 2:3:3:2 cadence.
24A has a different meaning in the HVR-V1/Z5/Z7 and S270 NTSC models. These camcorder’s “24A” setting embeds markers in the HDV1080/60i recorded stream in order for the NLE software to identify and remove 2:3 pull-down frames. Once the NLE software removes the pull-down fields, full progressive 23.98 editing is possible on the timeline.
Note that interruption of video, audio and TC may occur in between clips in the “24A” setting playback. Non compatible NLE may lose one or two seconds at the head of each clip. In this case, it is recommended to allow for longer pre-roll or to use the HVR-MRC1 Memory Recording Unit or HVR-DR60 Hard Disk Recording Unit for file importing.
While the compatible NLE software can effectively remove the 2:3 pull-down frames during capture by using this marker signal, some application software such as Cineform Aspect HD analyzes the video and removes the unwanted frames, then converts the video to 23.98p without needing the marker signal. But it may take longer than the workflow with the compatible NLE software.
*There is no “24A” setting for DV and DVCAM recording modes.
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◆◆◆ HDV Native Progressive Recording Format
An Optional Specification in HDV Format The HDV native progressive recording format is defined as an option of HDV1080i specification. There are three types of frequency, 24(23.98), 25 and 30 (29.97) frames / sec. The compatible Sony’s HDV products have the following logo :
Products without this logo can not playback the tape recorded in this format or can not accept the HDV native progressive i.LINK stream.
Name of Specifications HDV 720p Specification HDV 1080i Specification Media Same as DV format (DV cassette tape) Video Video Signal 720/60p, 720/30p 1080/60i, 1080/50i 720/50p, 720/25p Optional 720/24p 1080/30p, 1080/25p, 1080/24p Number of Pixels 1280 x 720 1440 x 1080 (Horizontal x Vertical) Aspect Ratio 16:9 Compression MPEG2 Video Profile & Level: MP@H-14 (in case of 720/60p and some 720/50p:MP@HL) Sampling Frequency for Luminance 74.25MHz 55.7MHz Sampling Format 4:2:0 Quantization 8 bit (both luminance and chrominance) Bit rate after Compression Approximately 19Mbps Approximately 25Mbps Audio Compression Mpeg1 Audio Layer II Sampling Frequency 48kHz Quantization 16 bits Bit rate after Compression 384kbps Audio Mode Stereo (2 channels) Optional Audio Recording PCM MPEG2 Audio Layer II (2 channels or 4 channels, can be (4 channels) simultaneously recorded with MPEG1 Audio Layer II 2 channels System Data Format MPEG2 Systems Stream Type Transport Stream Packetized Elementary Stream Stream Interface IEEE1394 (MPEG2-TS)
Compression Structure The MPEG-2 compression is done in the 15 GOP structure for 1080/25p and 30p as well as 1080/50i and 60i. On the other hand, the compression is done in 12 GOP structure for 1080/24p.
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For 1080/50i/60i/25p/30p
1GOP=15 frames 1GOP=15 frames
•••
For 1080/24p
1GOP=12 frames 1GOP=12 frames
Output Signal (in HVR-Z5, Z7, S270, M15A, M25A, M35) The i.LINK connector can output the HDV native progressive signal. For other connectors such as HDMI and SDI, the progressive signals are converted to interlace signals to be output. The 2-3 pull-down is used for 24P.
Recorded and Output TimeCode (in HVR-Z5, Z7, S270, M15A, M25A, M35) For 25p and 30p, the time code is recorded within the video in the cycle of 25 frames/sec. or 30 frames/sec. as well as 50i and 60i respectively. For 24p, the time code is based on the 30 frames/sec. cycle because the HDV native 24p format was developed using 1080/60i specification. So it is necessary to drop one frame for every five frames in terms of time code. The output signal from the i.LINK connector has the source timecode. The missing number of time codes are inserted in the output interlace signal from other connectors or down-converted DV signal.
Recorded 24p image and time code
1Sec
1GOP 1GOP
Time code 012356781011121315 16 17 18 20 21 22 23 25 26 27 28 image ABCDE FGHI JKLMNOPQRS TUVWX
24p to 60i Converted 60i image and time code
1Sec
1GOP 1GOP
Time code 01234 56789 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 image AABBBCCDDDE E E F FGGHHH I I J JJKKL L LMMN N N OOPPPQQ RRRS S T T T UUVVVWWXXX
Interpolated TC Interpolated TC Interpolated TC Interpolated TC Interpolated TC Interpolated TC
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◆◆◆ HDV Compression HDV compresses the video signal to fit it onto the DV tape. High definition comprises much more data than standard definition. Therefore the compression system needs to be very advanced. The techniques used are similar to those used by DV and MPEG2 compression. HDV compression can be divided into two basic sections, inter-frame coding and intra-frame compression. Although these two names are very similar, they are very different in practice.
The Concept of Entropy and Redundancy All video signals consist of a mixture of entropy and redundancy. Entropy is the information within the video signal that needs to be retained. If any entropy is lost, the quality of the image is reduced.
270Mbps
Redundancy Idealised Data rate
Realistic 2:1 compression Imperfect 2:1 compression
Perfect 10:1 compression Entropy
10:1 compression
0Mbps Simple Complex Complexity
Redundancy is the information within the video signal than can be removed without reducing the quality of the image.
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HDV Progressive Primer
a1 a2 a3 a4 a5 a6 a7 a8 DC a1 a2 a3 a4 a5 a6 a7 a8 b1 b2 b3 b4 b5 b6 b7 b8 b1 b2 b3 b4 b5 b6 b7 b8 Inverse c1 c2 c3 c4 c5 c6 c7 c8 DCT DCT c1 c2 c3 c4 c5 c6 c7 c8 d1 d2 d3 d4 d5 d6 d7 d8 d1 d2 d3 d4 d5 d6 d7 d8 e1 e2 e3 e4 e5 e6 e7 e8 e1 e2 e3 e4 e5 e6 e7 e8 f1 f2 f3 f4 f5 f6 f7 f8 f1 f2 f3 f4 f5 f6 f7 f8 g1 g2 g3 g4 g5 g6 g7 g8 g1 g2 g3 g4 g5 g6 g7 g8 h1 h2 h3 h4 h5 h6 h7 h8 h1 h2 h3 h4 h5 h6 h7 h8
Examples Big number somewhere here
DCT DCT
Big number somewhere here Big number Big number somewhere here somewhere here
DCT DCT
Big number Big number somewhere here somewhere here
DCT DCT
The amount of redundancy and entropy varies throughout a video sequence, and some sequences contain more entropy than others. Any video compressor aims to reduce the amount of information by removing redundancy only, thus maintaining the quality of the sequence. Some compression systems are better than others, and some remove a certain amount of entropy as well as redundancy in order to reduce the overall amount of information sufficiently to record to tape.
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HDV Progressive Primer
Inter-frame Coding Inter-frame coding compares one frame with another to remove redundant information. In most video sequences each video frame is very similar to its neighbour. There are two types of comparison, a P frame and a B frame. A P frame is a comparison to the previous frame only, and a B frame is a comparison to the previous frame and the next frame. Both P and B frames significantly reduce entropy and increase redundancy, but B frames result in less entropy than P frames and are therefore more efficient. Inter-frame coding does not reduce the amount of data at all. Instead it increases the amount of redundancy and reduces the amount of entropy. The resulting frame is then passes through Intra ?frame compression (described below) which dramatically reduces the total amount of data in each frame with no loss, much more effectively than simply using Intra-frame compression on its own.
Intra-frame Compression Intra-frame compression compresses each frame within itself, without comparison to any other frames. This is accomplished by using a sequence of processes which rearrange the data or replace it with smaller codes.
Discrete Base band Zig-zag Entropy Data Compressed Cosine Quantisation Input Scanning Coding Buffer output Transform
Discrete Cosine Transform (DCT) The first process in intra-frame compression is DCT. This process cuts the video frame into blocks of 8 by 8 pixels. Each block is processed separately. DCT does not reduce the amount of data at all. Instead it replaces each block with 64 numbers called coefficients. These coefficients describe how the original pixels change across the block. Any block with slow or gradual change will result in larger coefficients in the top left corner of the DCT block. Fast horizontal change results in high coefficients in the top right corner. Fast vertical change results in large coefficients in the bottom left corner. Various rates of change and angles of change result in various coefficients spread across the block. DCT is entirely lossless. The 64 coefficients can be replaced with their original 64 pixels with not loss of quality.
Entropy Coding This stage in the intra-frame compressor replaces coefficients with shorter codes. Entropy coding uses a look-up table of coefficients and codes, based on extensive research into many different types of video sequence. Entropy coding is the heart of any intra-frame compressor. It is entirely lossless. The codes can be replaced with the original coefficients with no loss of quality. If the entropy coder is able to reduce the amount of data sufficiently, the video signal can be recorded to tape with no overall loss of quality at all.
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HDV Progressive Primer
Data Buffer The data buffer acts a little like a gate-keeper. It stores the data from the entropy coder and prepares it for recording to tape. It also checks that the entropy coder has been able to reduce the overall amount of data sufficiently to fit on the tape. If it has, all is well and the data is recorded to tape. If not, then the data buffer sends a signal back to the Quantiser requesting it to remove entropy to allow the data to fit onto the tape.
Quantiser The quantiser is the single process in the whole compressor that reduces quality. It acts under control from the Data Buffer and divides coefficients to reduce the overall amount of data. This effectively removes entropy and therefore reduces quality. The Quantiser therefore attacks those coefficients first that do not affect the overall quality too much. High frequency coefficients are divided first. If this is not enough, lower frequency coefficients are divided.
Building an HDV Stream The HDV compressor uses both Intra-frame and Inter-frame compression. Compression is performed in a sequence of video frames called a Group of Pictures (GOP). The first frame in each GOP is an I frame, one frame compressed within itself with no reference to any other frames. The next two frames are B frames. Compared to the I frame before and the next P frame, and then Intra-frame compressed, these frames contains significantly less data than the I frame with little loss of quality.
— — — — — SUM SUM SUM SUM SUM
Intra-Frame Intra-Frame Compression Compression
Intra-Frame Intra-Frame Intra-Frame Intra-Frame Intra-Frame Compression Compression Compression Compression Compression
The forth frame is a P frame, compared to the I frame before intra-frame compression this frame results in slightly more data than the two B frames but still significantly less data than the I frame. The sequence is then repeated with two B frames and a P frame until 12 frames have been processed. A new GOP is then started by compressing a single I frame.
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