1、 CEA Bulletin Active Format Description (AFD) Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream, July 2011 10. IEC 61880 Video Systems (525/60) video and accompanied data using the vertical blanking intervalAnalogue interface, 1998
2、11. SMPTE RP 202-2008, Video Alignment for MPEG-2 Coding, April 2008 2.2 Informative Reference Acquisition ATSC Standards: Advanced Television Systems Committee, 1776 K Street N.W., Suite 200, Washington, DC 20006; Phone 202-872-9160; Internet http:/www.atsc.org/ CEA Standards and Bulletins: Global
3、Engineering Documents, World Headquarters, 15 Inverness Way East, Englewood, CO 80112-5776; Phone 800-854-7179; Internet http:/; Email HDMI HDMI Licensing, LLC, 1060 E. Arques Avenue, Suite 100, Sunnyvale, CA 94085; URL http:/www.hdmi.org EIAJ Standards: Available from Japan Electronics and Informa
4、tion Technology Industries Association (JEITA). Internet http:/www.jeita.or.jp/eiaj/english/ IEC Standards: International Electrotechnical Commission. E-mail: inmailiec.ch. Internet http:/www.iec.ch/ DVB Standards: Available from European Telecommunications Standards Institute. Internet: http:/www.e
5、tsi.org/ CEA-CEB16-A 2 SMPTE Standards, Recommended Practices and Engineering Guidelines: Society of Motion Picture and Television Engineers. Internet: http:/www.smpte.org/ 3 Acronyms AFD Active Format Description ATSC Advanced Television Systems Committee CCO center cut-out CEA Consumer Electronics
6、 Association CGMS-A Copy Generation Management System-Analog CVI Component Video Interface DTV Digital Television DVB Digital Video Broadcasting ETSI European Telecommunications Standards Institute HD High Definition HDMI High Definition Multimedia Interface IEC International Electrotechnical Commis
7、sion ISO International Organization for Standardization JEITA Japan Electronics and Information Technology Industries Association MPEG Motion Picture Experts Group NTSC National Television Systems Committee II RP Recommended Practice SMPTE Society of Motion Picture and Television Engineers SD Standa
8、rd Definition STB Set-top Box TS Transport Stream VBI Vertical Blanking Interval WSS wide-screen signaling 4 Definition of Terms Active Format Description A 4-bit data field that conveys how the image should be displayed in order to best maintain the artistic intent of its creators. Active Image The
9、 useful portion of the image. The Active Image excludes letterbox bars and pillarbox bars. bar data Data that enable computation of regions of the image that are outside of the Active Image, for example areas of zero or uniform luminance. Total Image The entire image area including both Active Image
10、 and letterbox bars or pillarbox bars. Coded Frame As used in CEA-CEB16-A, a compressed signal representing a rectangular array of pixels containing an image that may, in whole or part, be eventually rendered onto a display. Display Aspect Ratio The physical width-to-height ratio of the light-emitti
11、ng area of the display device. Picture As used in CEA-CEB16-A, an uncompressed signal representing an rectangular array of pixels containing an image that may, in whole or part, be rendered onto a display. letterbox A Total Image having horizontal bars, usually black, present at the top and bottom.
12、pillarbox A Total Image having vertical bars, usually black, present at the left and right. postage stamp image A Total Image where both letterbox bars and pillarbox bars are present. scale To change the Picture size along both axes by multiplying the same constant. In CEA-CEB16-A, the term scaling
13、does not include non-linear or anamorphic conversions. CEA-CEB16-A 3 5 Background and Overview Broadcast standards in current use for television offer two aspect ratios for the Coded Frame: 4:3 and 16:9. But when source material is placed into the Coded Frame, exact matching of the aspect ratios is
14、not always possible. For example, a 16:9 Active Image may be placed within a 4:3 Coded Frame, or a 4:3 Active Image within a 16:9 Coded Frame, resulting in “letterbox” or “pillarbox” display presentations, respectively. These effects also occur when the aspect ratios of the Pictures do not match the
15、 aspect ratios of the physical displays. Content creators have employed framing techniques to optimize the presentation of their content on various displays. A producer may for example, shoot scenes using a 16:9 Total Image while “protecting“ a 4:3 Active Image containing all “essential or useful” i
16、nformation. The result may then be presented on both 16:9 and 4:3 displays with minimal loss of content. In many display products, user-selectable viewport modifiers such as zoom and stretch are offered since a single fixed-display format may not be optimal for all viewers or all content. These vari
17、ables in the production, coding, and display of content may lead to sub-optimal presentations. This document provides recommendations in an attempt to mitigate certain undesirable display effects. AFD and bar data as described below may be used by display devices to optimize automatically the presen
18、tation of visual content. Aspect ratio and AFD signaling within the ATSC transport multiplex can indicate to the receiving device that certain portions of the Total Image do not carry essential information and thus may be cropped. The syntax and semantics of the AFD were originally described in Anne
19、x B of the DVB document “Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream” 9. The coding of the 4-bit active_format field from this specification is reprinted here in Annex A. ATSC Digital Television Standard A/53 Part 4 1, reitera
20、tes this information and defines the carriage of AFD in the ATSC video elementary stream, while introducing the related bar data as a refinement. Bar data signals the extents of the letterbox bars or pillarbox bars, specified in numbers of video lines or pixels respectively, and provides a finer res
21、olution mechanism for the signaling of non-essential areas in the Total Image, especially in cases where the Active Images aspect ratio is other than 4:3, 14:9 or 16:9. Subtracting the bar areas from the Total Image yields an Active Image or “area of interest” that represents essential content. Alth
22、ough this document provides guidance for content involving Active Images having 14:9 aspect ratios, such content is not likely to be encountered. AFD and bar data are not mutually exclusive alternatives, but should be applied in concert to allow receiving and display devices to determine the proper
23、framing of the image and the exact extent of its Active Image boundaries. The relationship between AFD and bar data is discussed in ATSC A/53 Part 4 1 Section 6.2.5 and their use is explained in this document. 5.1 Aspect Ratios In the consumer electronics (CE) industry, aspect ratios are typically e
24、xpressed using HORIZONTAL:VERTICAL notation and include the ratios 4:3, 14:9, 16:9 and wider than 16:9. The aspect ratio of the various components of a Total Image delivery system may vary. For example, the aspect ratio of the Coded Frame on the compressed interface, the Picture on an uncompressed i
25、nterface, the Active Image (i.e. useful area) within a Coded Frame or Picture, the physical screen of the display device CEA-CEB16-A 4 may not all be the same. Therefore, a Total Image may encounter different aspect ratios as it flows from a creator to a viewer, perhaps as it is transferred via Code
26、d Frame through a packaged-media, satellite, cable, terrestrial broadcast, or Internet-based delivery system to a set-top-box or player then over an uncompressed analog or digital interface connecting local components within the home (see Section 5.2 below). Where aspect ratio transitions occur, Tot
27、al Images may need to be cropped, padded and/or scaled in order to adapt to the aspect ratio at each particular processing point. Active Format Description and bar metadata signaling can be used to help optimize this mapping process, by indicating incoming aspect ratio and which portions of an incom
28、ing Coded Frame or Picture is intended to be displayed. Improper interpretation of (or even ignoring) such metadata signals may lead to sub-optimal presentations. This document provides recommendations in an attempt to mitigate certain undesirable effects. B r o a d c a s tO RW e b c a s tO RP a c k
29、 a g e d M e d i aR e c e i v e r O RP l a y e rO RG a m e C o n s o l eT o t a l I m a g e ,C o d e d F r a m e ,A c t i v e I m a g e + b a r sA c t i v e I m a g e a s p e c t r a t i oD i s p l a yT o t a l I m a g e ,P i c t u r e , A c t i v e I m a g e + b a r sA c t i v e I m a g e a s p e c
30、 t r a t i oD i s p l a y A s p e c t R a t i oC o n t e n tC o m p r e s s e d I n t e r f a c e( e . g . A T S C )U n c o m p r e s s e d I n t e r f a c e( e . g . C E A - 8 6 1 )Figure 1 System Block Diagram Section 7.2.2 covers the 16:9 aspect ratio case. The tables show, in the leftmost column
31、, the format of the incoming Coded Frame. These tables also show, for each incoming signal format, the aspect ratio and AFD setting, the recommended decoder response, and the recommended signaling across uncompressed analog or digital interfaces on the decoder output. Recommended receiver behavior i
32、s documented for eight of the 16 possible AFD states. These are expected to be the only ones likely to be encountered in practice. For all other states, AFD should be treated as if not present. The information contained in the tables may be the same for some AFD values because any of the values in t
33、his range may be encountered. There is no illustration for 0000, as its shape is determined by bar data, if present, and either letterbox or pillarbox bars may be used depending on the aspect ratio of the incoming image. See Sections 5.1.3 and 5.1.4. Except for 0100, defined AFD values in the range
34、0001 to 0111 should be rarely encountered; these values are not addressed in CEA-CEB16-A. CEA-CEB16-A 9 In some cases, the recommendation involves display processing in response to aspect ratio and AFD signaling to create the optimum display. In other cases, processing on the source side can be done
35、 to output the optimum signal for direct display (to address the case that the display is unable to perform reformatting). CEA-CEB16-A recommends the resulting images illustrated. Other display options are shown, but not recommended. In the tables in Sections 7.2.1 and 7.2.2, the rows relating to NT
36、SC interfaces (as diagrammed in Figures 2 and 3) are highlighted with gray shading. The rows displayed with white background relate to interfaces capable of re-encapsulating complete AFD and barcode data. The “n.a.” (“not applicable”) notation indicates the signaling does not apply to that type of i
37、nterface. In the image format illustrations in the tables in Sections 7.2.1 and 7.2.2, the meaning of the shaded areas is: Closed circles are provided as an aid to visualization. See also Annex B. In the tables in Sections 7.2.1 and 7.2.2, the use of the word Default in the Comments columns means it
38、 is a receiver recommended initial default condition, i.e., after first receiving the aspect ratio signal and before any user aspect ratio control selections are made at the receiver. Numerical values for the geometrical relationships of the aspect ratios are shown in Annex B. 7.2.1 Transmissions wi
39、th MPEG = 4:3 Table 2 through Table 12 provides recommendations for images transmitted in a 4:3 Coded Frame. Indicates the portion of the Active Image which may be cropped for optimum display as appropriate to the aspect ratio of the display screen Indicates a matte, often black, which is transmitte
40、d as part of the video Coded Frame to fill the area outside the Active Image Video/static level, typically black, generated by the receiver (either in the decoder or display) CEA-CEB16-A 10 Transmission Receiver Transmitted Signaling Display Aspect Ratio Receiver Format Conversion Output Signaling D
41、isplay Action Display Appearance Comments MPEG 4:3 AFD 0100 (Note 1) WSS Line 20 Bit 1,2 CEA 861 R3R0 CEA 805 R3R0 Greater than 16:9 Letterbox Image 4:3 None 01 4:3 Letterbox n.a. n.a. Substitute black or gray in area outside 16:9 if desired None n.a. 0100 + bar data (Note 2) 0100 + bar data (Note 2
42、) Substitute black or gray in bar areas if desired 16:9 None 01 16:9 Letterbox n.a. n.a. Scale image to match horizontal display width None n.a. 0100 + bar data (Note 2) 0100 + bar data (Note 2) Scale image to match horizontal display width. Substitute black or gray in bar areas if desired Note 1Thi
43、s AFD value is expected to be used only when the aspect ratio of the content is greater than 16:9 (1.77:1). One example is content originally created for the cinema, such as a scope feature with an aspect ratio of 2.40:1. Note 2When bar data is available. Table 2 MPEG 4:3 AFD Value 0100 CEA-CEB16-A
44、11 Transmission Receiver Transmitted Signaling Display Aspect Ratio Receiver Format Conversion Output Signaling Display Action Display Appearance Comments MPEG 4:3 AFD 1000 WSS Line 20 Bit 1,2 CEA 861 R3R0 CEA 805 R3R0 4:3 Full Frame Image 4:3 None 00 4:3 Normal n.a. n.a. None None n.a. 1000 1000 No
45、ne 16:9 None 00 4:3 Normal n.a. n.a. Add pillarbox bars User options may give different display appearances None n.a. 1000 1000 Add pillarbox bars User options may give different display appearances Table 3 MPEG 4:3 AFD Value 1000 CEA-CEB16-A 12 Transmission Receiver Transmitted Signaling Display As
46、pect Ratio Receiver Format Conversion Output Signaling Display Action Display Appearance Comments MPEG 4:3 AFD 1001 WSS Line 20 Bit 1,2 CEA 861 R3R0 CEA 805 R3R0 4:3 Full Frame Image 4:3 None 00 4:3 Normal n.a. n.a. None None n.a. 1001 1001 None 16:9 None 00 4:3 Normal n.a. n.a. Add pillarbox bars U
47、ser options may give different display appearances None n.a. 1001 1001 Add pillarbox bars User options may give different display appearances Table 4 MPEG 4:3 AFD Value 1001 CEA-CEB16-A 13 Transmission Receiver Transmitted Signaling Display Aspect Ratio Receiver Format Conversion Output Signaling Di
48、splay Action Display Appearance Comments MPEG 4:3 AFD 1010 WSS Line 20 Bit 1,2 CEA 861 R3R0 CEA 805 R3R0 16:9 Letterbox Image 4:3 None 01 4:3 Letterbox n.a. n.a. Substitute gray for transmitted matte if desired No scaling None n.a. 1010 1010 Substitute gray for transmitted matte if desired No scalin
49、g 16:9 None 01 4:3 Letterbox n.a. n.a. Scale image to match horizontal display width None n.a. 1010 1010 Scale image to match horizontal display width Table 5 MPEG 4:3 AFD Value 1010 CEA-CEB16-A 14 Transmission Receiver Transmitted Signaling Display Aspect Ratio Receiver Format Conversion Output Signaling Display Action Display Appearance Comments MPEG 4:3 AFD 1011 WSS Line 20 Bit 1,2 CEA 861 R3R0 CEA 805 R3R0 14:9 Letterbo
