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cgms a wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 history 2 applications 3 standardization toggle standardization subsection 3 1 contradicting type a standards 3 2 cea 805 cgms a type b confusion 4 signalling 5 references 6 external links toggle the table of contents cgms a 3 languages català deutsch français edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia copy protection mechanism for analog tv signals this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources cgms a news newspapers books scholar jstor december 2007 learn how and when to remove this message copy generation management system analog cgms a is a copy protection mechanism for analog television signals it consists of a waveform inserted into the non picture vertical blanking interval vbi of an analogue video signal if a compatible recording device for example a dvd recorder detects this waveform it may block or restrict recording of the video content it is not the same as the broadcast flag which is designed for use in digital television signals although the concept is the same 1 there is a digital form of cgms specified as cgms d which is required by the dtcp 5c protection standard history edit cgms a has been in existence since 1995 and has been standardized by various organizations including the iec and eia cea it is used in devices such as pvrs dvrs dvd players and recorders d vhs and blu ray recorders as well certain television broadcasts more recent tivo firmware releases comply with cgms a signals applications edit implementation of cgms a is required for certain applications by dvd cca license d vhs and some dvd recorders comply with cgms a signal on analog inputs the technology requires minimal signal processing where the source signal is analogue e g vhs analogue broadcast the cgms a signalling may be present in that source where the source signal is digital e g dvd digital broadcast then the copy control information cci is carried in metadata in the digital transport or program stream and a compliant hardware device e g a dvd player will read that data and encode it into the analogue video signal generated within the device itself there is no blanket legal requirement for devices which record video to detect or act upon the cgms a information for example the digital millennium copyright act does not require manufacturers of consumer electronics telecommunications or computing equipment to design their products affirmatively to respond to any particular technological measure 2 standardization edit cgms a is standardized through the iec cea eia j and etsi as follows video format standard line number s bit number s type 480i60 525i ntsc iec 61880 20 283 7 8 a 480i60 525i ntsc cea 608 284 4 3 480p60 525p eia j cpr1204 1 41 a 480p60 525p iec 61880 2 41 7 8 a 480p60 525p cea 805 41 7 8 a 480p60 525p cea 805 40 38 g 0 39 g 1 b 720p60 cea 805 24 7 8 a 720p60 cea 805 23 38 g 0 39 g 1 b 1080i60 cea 805 19 582 7 8 a 1080i60 cea 805 18 581 38 g 0 39 g 1 b 576i50 625i pal en 300 294 23 12 13 576p50 625p iec 62375 43 12 13 in all these standards the cgms a information is only two out of many bits of information that are defined on 60 hz systems commonly known as ntsc the system is highly extensible though beyond the cgms a bits only the aspect ratio of the video signal and the analog protection system aps bits are commonly used the signalling is typically present on every video frame but cea 805 d states that the transmission rate for any given packet type defined in cea 805 d shall be at least once every three frames meaning that in theory for two out of three frames different header values can be used to send data not defined in the standard type a signalling 20 bits in total the only type defined for 480i offers some extensibility by re using the 14 data bits via one of the 14 undefined values for the four header bits type b signalling 134 bits in total already defines bits to carry an active format description colorimetry redistribution control and a pixel accurate definition of the location of any letterbox or pillarbox bars in the image plus two bytes reserved for future use different header bit values may also be used for further extensibility on 50 hz systems commonly though incorrectly known as pal the bits that are widely used and interpreted as cgms a are not named as such and are added at the end of an existing signalling standard originally created for the palplus video format but still in common use in europe in standard pal video called widescreen signaling contradicting type a standards edit some references quote eia j cpr1204 1 as the authoritative reference for cgms a on 480p60 525p systems since this was the first published standard to mention cgms a on 480p this eia j document does not define the meaning of the bits only their timing on the analogue video signal the 480p signalling is based on the existing 480i standard but with a double speed clock and iec 61880 2 formalises this by defining bit meanings which are the same as for 480i however cea 805 re defines the aspect ratio signalling bits hence 480p type a line 40 cgmms a data generated in accordance with cea 805 cannot signal the aspect ratio of the video image and in this way is incompatible with the same data generated in accordance with iec 61880 2 and is no longer a straight double speed clock version of the 480i standard cea 805 cgms a type b confusion edit cea 805 is now on its fourth major version cea 805 d and there have been errata issued to at least one version cea 805 d recognises that in respect of type b signalling earlier versions of the standard were unclear regarding the order of bits as represented in the analogue video signal vs as used for the crc calculation and also which bits were to be used for the crc calculation issue d requires sink devices to perform multiple crc calculations for type b signalling taking account of various possible implementations in source devices there is no such confusion surrounding type a signalling signalling edit cea 608 b specifies meaning of the 7 bit field placed on the data lines the bits 4 and 3 contain the cgms a values the bits 2 and 1 contain the analog protection system aps value the bit 0 is the analog source bit asb specifying if the signal originates from a pre recorded material bits 5 and 6 are reserved cgms a is signalled by 2 bits in the vertical blanking interval vbi signal of analog television broadcasts according to the following matrix 0 0 copyfreely unlimited copies may be made of the content 0 1 copynomore one generation of copies has already been made no further copying is allowed 1 0 copyonce one generation of copies may be made 1 1 copynever no copies may be made of the content copynomore was not a part of the original standard the 0 1 value originally was reserved references edit techdirt microsoft it s not the broadcast flag it s a different flag the digital millennium copyright act of 1998 u s copyright office summary http www copyright gov legislation dmca pdf external links edit copy generation management system analog powerpoint microsoft videoparameters structure for windows gdi video connections techdirt microsoft it s not the broadcast flag it s a different flag v t e broadcast encryption and digital rights management conditional access cablecard conditional access system renewable security dvb common interface csa conditional access module dvb cpcm ftv syndication smart cards and encryption biss cisco videoscape videoguard conax irdeto cryptoworks digicipher hdcp keyfly nagravision powervu ras seca mediaguard verimatrix viaccess digital video disc content scramble system css advanced access content system aacs bd drm authorized domain b cas broadcast flag data security card sharing fta pirate decryption analogue broadcast encoding b mac cgms a eurocrypt leitch oak orion videocipher videocrypt see also free to view and pay television v t e video formats television analog 405 lines system a 525 lines system m color systems ntsc ntsc j clear vision pal m b mac 625 lines system b c d g h i k l n color systems pal pal n palplus secam mac 819 lines system e f 1125 lines muse 1250 lines hd mac audio btsc mts eiaj nicam sap sound in syncs zweikanalton a2 igr hidden signals captioning cgms a epg gcr pdc teletext vbi veil vit vitc wss xds historical pre 1940 mechanical television 180 line 343 line 375 line 441 line 455 line 567 line field sequential color system oskm digital interlaced sdtv 480i 576i hdtv 1080i progressive ldtv 1seg 240p 288p edtv 480p 576p hdtv 720p 1080p uhdtv 4k 8k mpeg 2 video atsc dvb dvb 3d tv isdb dtmb abs s avs cmmb avs note 1 dtmb abs s mpeg 4 visual mobaho note 2 mpeg 4 avc atsc a 72 cmmb dmb dtmb dvb sbtvd 1seg mobaho note 2 avs2 note 1 abs s mpeg h hevc atsc 3 0 dvb hd dmb isdb s3 dtmb audio ac 3 5 1 ac 4 dts dra mpeg 1 audio layer ii mpeg multichannel pcm lpcm aac he aac mpeg h 3d audio hidden signals afd broadcast flag captioning cpcm epg teletext 1 2 also used in china s dvb s s2 network 1 2 defunct technical issues 14 9 compromise broadcast safe digital cinema dci display motion blur mpeg transport stream reverse standards conversion standards conversion television transmitter test card video on demand video processing widescreen signaling templates analogue tv topics retrieved from https en wikipedia org w index php title cgms a oldid 1350341974 categories digital rights management standards digital television high definition television television technology hidden categories articles with short description short description is different from wikidata articles needing additional references from december 2007 all articles needing additional references this page was last edited on 21 april 2026 at 11 13 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile 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