ID3 tag manager

ID3 tag supervisor

This document is a casual standard and replaces the ID3 tag supervisor.3.ZERO standard [ID3 tag manager]. A FORMAL usual will use some other revision quantity even if the content is similar to record. The contents in this record may amendment for clarifications but by no means for extra or altered functionallity. Distribution of this file is unlimited. Summary This file describes the principle structure of ID3v, which is a revised model of the ID3 tag manager informal standard [ID3 tag manager] model 2.THREE.0. The ID3 tag manager provides a flexible way of storing audio meta knowledge within the audio report itself. the tips is also technical data, comparable to equalisation curves, as well as identify, performer, copyright and so forth. ID3v is meant to be as close as imaginable to ID3 tag manager.3.ZERO so as to allow for implementations to be revised as easily as possible. 1. Desk of contents Status of this report Summary 1. Table of contents 2. Conventions in this report 2. Usual review THREE. ID3 tag manager assessment 3.1. ID3 tag supervisor header 3.2. ID3 tag supervisor prolonged header THREE.THREE. Padding THREE.FOUR. ID3 tag manager footer FOUR. ID3 tag supervisor frames evaluation 4.1. Frame header flags FOUR.1.1. Frame standing flags FOUR.1.2. Frame layout flags FIVE. Tag region 6. Unsynchronisation 6.1. The unsynchronisation scheme 6.2. Synchsafe integers 2. Conventions in this report Textual Content inside of ”” is a text string precisely as it appears in a tag. Numbers preceded with $ are hexadecimal and numbers preceded with % are binary. $xx is used to suggest a byte with unknown content. %x is used to indicate a bit with unknown content. probably the most vital bit (MSB) of a byte is known as ‘bit 7’ and the least significant bit (LSB) is known as ‘bit 0’. A tag is the whole tag defined in this document. A frame is a block of knowledge within the tag. The tag contains a header, frames and non-compulsory padding. A field is a piece of knowledge; one value, a string and the like. A numeric string is a string that contains the characters “0123456789” handiest. the key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOW NOT”, “WILL HAVE TO”, “IS NOT GOING TO”, “ADVISABLE”, “WOULD POSSIBLY”, and “NOT OBLIGATORY” on this file are to be interpreted as described in RFC 2119 [KEYWORDS]. THREE. ID3 tag manager evaluate ID3 tag manager is a general tagging structure for audio, which makes it conceivable to retailer meta data in regards to the audio inside the audio document itself. The ID3 tag defined on this document is mainly targeted at recordsdata encoded with MPEG-1/2 layer I, MPEG-1/2 layer II, MPEG-1/2 layer III and MPEG-2.5, but may work with different sorts of encoded audio or as a stand alone format for audio meta data. ID3 tag supervisor is designed to be as versatile and expandable as imaginable to satisfy new meta data needs that would stand up. to succeed in that ID3 tag manager is built as a box for several knowledge blocks, known as frames, whose layout need not be known to the software that encounters them. at the get started of each frame is an unique and predefined identifier, a dimension descriptor that permits instrument to skip unknown frames and a flags box. The flags describes encoding main points and if the frame should stay in the tag, will have to or not it's unknown to the software, if the record is altered. The bitorder in ID3 tag supervisor is most significant bit first (MSB). The byteorder in multibyte numbers is most significant byte first (e.g. $12345678 can be encoded $12 34 56 78), also referred to as big endian and community byte order. Total tag structure: —-—-—-—-—-— | Header (10 bytes) | —-—-—-—-—-— | Prolonged Header | | (variable length, OPTIONAL) | —-—-—-—-—-— | Frames (variable period) | —-—-—-—-—-— | Padding | | (variable period, NOT OBLIGATORY) | —-—-—-—-—-— | Footer (10 bytes, NON-COMPULSORY) | —-—-—-—-—-— Typically, padding and footer are jointly unique. See details in sections THREE.3, THREE.4 and FIVE. 3.1. ID3 tag manager header the first part of the ID3 tag manager tag is the 10 byte tag header, laid out as follows: ID3 tag supervisor/file identifier “ID3” ID3 tag manager model $04 00 ID3 tag supervisor flags %abcd0000 ID3 tag manager size 4 * %0xxxxxxx the first three bytes of the tag are always “ID3”, to signify that this is an ID3 tag supervisor tag, immediately adopted by the 2 version bytes. the first byte of ID3 tag supervisor model is its top model, while the second byte is its revision quantity. in this case that is ID3v. All revisions are backwards compatible even as prime variations are not. If tool with ID3v and below strengthen will have to come upon version five or higher it's going to simply forget about the whole tag. Version or revision will never be $FF. The model is followed through the ID3 tag manager flags box, of which these days four flags are used. a – Unsynchronisation Bit 7 within the ‘ID3 tag supervisor flags’ indicates whether or now not unsynchronisation is applied on all frames (see section 6.1 for details); a collection bit indicates usage. b – Extended header the second one bit (bit 6) signifies whether or not the header is followed through an extended header. The extended header is defined in segment 3.2. a set bit indicates the presence of a longer header. c – Experimental indicator The third bit (bit FIVE) is used as an ‘experimental indicator’. This flag SHALL always be set while the tag is in an experimental stage. d – Footer present Bit 4 indicates that a footer (section THREE.FOUR) is present on the very end of the tag. a set bit signifies the presence of a footer. all of the other flags have to be cleared. If certainly one of those undefined flags are set, the tag may not be readable for a parser that does not recognize the flags serve as. The ID3 tag manager tag size is saved as a 32 bit synchsafe integer (section 6.2), making a general of 28 effective bits (representing as much as 256MB). The ID3 tag manager tag dimension is the sum of the byte period of the prolonged header, the padding and the frames after unsynchronisation. If a footer is provide this equals to (‘total dimension’ – 20) bytes, another way (‘overall dimension’ – 10) bytes. An ID3 tag manager tag will also be detected with the next development: $49 44 33 yy yy xx zz zz zz zz The Place yy is lower than $FF, xx is the ‘flags’ byte and zz is lower than $EIGHTY. THREE.2. Extended header The extended header contains data that can supply additional insight in the construction of the tag, however is not important to the proper parsing of the tag information; hence the prolonged header is non-compulsory. Prolonged header size FOUR * %0xxxxxxx collection of flag bytes $01 Extended Flags $xx The Place the ‘Extended header dimension’ is the dimensions of the entire prolonged header, saved as a 32 bit synchsafe integer. a longer header can therefore by no means have a size of fewer than six bytes. The extended flags field, with its measurement defined via ‘selection of flag bytes’, is outlined as: %0bcd0000 Each flag that is set within the prolonged header has information connected, which comes in the order during which the flags are encountered (i.e. the information for flag ‘b’ comes sooner than the information for flag ‘c’). Unset flags can't have any connected information. All unknown flags need to be unset and their corresponding data got rid of whilst a tag is modified. Each And Every set flag’s information begins with a period byte, which includes a value among 0 and 128 ($00 – $7f), followed by way of knowledge that has the field duration indicated through the period byte. If a flag has no hooked up knowledge, the price $00 is used as period byte. b – Tag is an replace If this flag is about, the existing tag is an update of a tag found earlier within the provide record or stream. If frames defined as distinctive are found within the present tag, they're to override any corresponding ones found in the earlier tag. This flag has no corresponding knowledge. Flag data period $00 c – CRC data present If this flag is about, a CRC-32 [ISO-3309] information is integrated within the extended header. The CRC is calculated on all the knowledge between the header and footer as indicated by the header’s tag period box, minus the prolonged header. Notice that this includes the padding (if there is any), but excludes the footer. The CRC-32 is saved as an 35 bit synchsafe integer, leaving the higher 4 bits always zeroed. Flag knowledge length $05 Overall body CRC 5 * %0xxxxxxx d – Tag restrictions For a few programs it might be wanted to restrict a tag in more ways than imposed via the ID3 tag manager specification. Observe that the presence of those restrictions doesn't impact how the tag is decoded, merely how it was once limited ahead of encoding. If this flag is about the tag is particular as follows: Flag knowledge period $01 Regulations %ppqrrstt p – Tag measurement restrictions 00 Not More than 128 frames and 1 MB general tag size. 01 Not More than SIXTY FOUR frames and 128 KB general tag measurement. 10 No More than 32 frames and 40 KB total tag size. 11 Not More than 32 frames and four KB overall tag dimension. q – Textual Content encoding regulations 0 No restrictions 1 Strings are just encoded with ISO-8859-1 [ISO-8859-1] or UTF-EIGHT [UTF-8]. r – Textual Content fields dimension regulations 00 No regulations 01 No string is longer than 1024 characters. 10 No string is longer than 128 characters. ELEVEN No string is longer than 30 characters. Observe that not anything is claimed about what number of bytes is used to symbolize the ones characters, since it is encoding dependent. If a text body consists of greater than one string, the sum of the strungs is restricted as stated. s – Image encoding regulations ZERO No regulations 1 Photographs are encoded only with PNG [PNG] or JPEG [JFIF]. t – Image size regulations 00 No restrictions 01 All pictures are 256×256 pixels or smaller. 10 All images are SIXTY FOUR×64 pixels or smaller. ELEVEN All photographs are exactly SIXTY FOUR×64 pixels, until required otherwise. 3.3. Padding It's OPTIONAL to include padding after the overall frame (at the end of the ID3 tag), making the size of all the frames together smaller than the dimensions given within the tag header. a possible function of this padding is to allow for including a couple of additional frames or amplify present frames inside the tag with no need to rewrite the entire report. the price of the padding bytes have to be $00. A tag MUST NEVER have any padding between the frames or among the tag header and the frames. Furthermore it MUST NOT have any padding when a tag footer is delivered to the tag. 3.4. ID3 tag supervisor footer to hurry up the process of finding an ID3 tag supervisor tag when looking out from the top of a document, a footer can also be delivered to the tag. It's REQUIRED to add a footer to an appended tag, i.e. a tag located after all audio data. The footer is a replica of the header, but with a distinct identifier. ID3 tag supervisor identifier “3DI” ID3 tag supervisor version $04 00 ID3 tag manager flags %abcd0000 ID3 tag supervisor dimension FOUR * %0xxxxxxx FOUR. ID3 tag supervisor frame review All ID3 tag supervisor frames includes one body header followed by way of one or extra fields containing the actual data. The header is usually 10 bytes and laid out as follows: Frame ID $xx xx xx xx (4 characters) Dimension FOUR * %0xxxxxxx Flags $xx xx The frame IDENTITY is made out of the characters capital A-Z and nil-9. Identifiers starting with “X”, “Y” and “Z” are for experimental frames and loose for everyone to use, without the desire to set the experimental bit in the tag header. Undergo in mind that somebody else might have used the similar identifier as you. All different identifiers are either used or reserved for future use. The frame IDENTIFICATION is adopted through a size descriptor containing the size of the data within the ultimate frame, after encryption, compression and unsynchronisation. the dimensions is apart from the frame header (‘general frame size’ – 10 bytes) and stored as a 32 bit synchsafe integer. in the frame header the dimensions descriptor is followed via two flag bytes. Those flags are defined in phase FOUR.1. there may be no fastened order of the frames’ appearance within the tag, despite the fact that it is favored that the frames are arranged so as of significance concerning the recognition of the document. An instance of such order: UFID, TIT2, MCDI, TRCK … A tag MUST contain no less than one frame. A body have to be a minimum of 1 byte large, except the header. If not anything else is claimed, strings, including numeric strings and URLs are represented as ISO-8859-1 [ISO-8859-1] characters in the vary $20 – $FF. Such strings are represented in body descriptions as <textual content string>, or <complete text string> if newlines are allowed. If nothing else is said newline character is forbidden. In ISO-8859-1 a newline is represented, while allowed, with $0A handiest. Frames that permit different sorts of textual content encoding contains a textual content encoding description byte. Possible encodings: $00 ISO-8859-1 [ISO-8859-1]. Terminated with $00. $01 UTF-16 UTF-16 encoded Unicode UNICODE with BOM. All strings within the comparable frame SHALL have the same byteorder. Terminated with $00 00. $02 UTF-16BE UTF-16 encoded Unicode UNICODE without BOM. Terminated with $00 00. $03 UTF-EIGHT UTF-8 encoded Unicode UNICODE. Terminated with $00. Strings depending on encoding are represented in frame descriptions as <text string in keeping with encoding>, or <full text string consistent with encoding> if newlines are allowed. Any empty strings of sort $01 which can be NULL-terminated will have the Unicode BOM adopted by a Unicode NULL ($FF FE 00 00 or $FE FF 00 00). The timestamp fields are based on a subset of ISO 8601. Whilst being as precise as imaginable the structure of a time string is yyyy-MM-ddTHH:mm:ss (yr, “”, month, “”, day, “T, hour (out of 24),, minutes, ”:”, seconds), however the precision could also be lowered through disposing of as many time signs as sought after. Therefore legitimate timestamps are yyyy, yyyy-MM, yyyy-MM-dd, yyyy-MM-ddTHH, yyyy-MM-ddTHH:mm and yyyy-MM-ddTHH:mm:ss. All time stamps are UTC. For intervals, use the reduce character as defined in 8601, and for multiple noncontiguous dates, use more than one strings, if allowed through the frame definition. the three byte language box, present in a number of frames, is used to describe the language of the body’s content material, in keeping with ISO-639-2 The language need to be represented in decrease case. If the language is not identified the string “XXX” have to be used. All URLs URL is also relative, e.g. “picture.png”, ”../doc.txt”. If a body is longer than it may be, e.g. having extra fields than specific in this document, that signifies that additions to the body have been made in a later version of the ID3 tag supervisor same old. this is mirrored by way of the revision number in the header of the tag. FOUR.1. Body header flags in the body header the dimensions descriptor is followed through two flag bytes. All unused flags must be cleared. the first byte is for ‘standing messages’ and the second byte is a layout description. If an unknown flag is ready within the first byte the body MUST NEVER be changed without that bit cleared. If an unknown flag is ready in the 2d byte the frame is likely not to be readable. A Few flags in the second byte indicates that additional knowledge is introduced to the header. Those fields of extra information is ordered because the flags that indicates them. The flags box is outlined as follows (l and o omitted as a result of ther resemblence to at least one and zero): %0abc0000 %0h00kmnp A Few frame format flags indicate that additional info fields are added to the frame. this information is brought after the body header and sooner than the frame knowledge in the related order as the flags that indicates them. I.e. the 4 bytes of decompressed measurement will precede the encryption means byte. These additions affects the ‘frame size’ field, but don't seem to be matter to encryption or compression. The default status flags setting for a frame is, except said another way, ‘preserved if tag is altered’ and ‘preserved if file is altered’, i.e. %00000000. 4.1.1. Frame status flags a – Tag modify preservation This flag tells the tag parser what to do with this frame if it's unknown and the tag is altered in any method. this is applicable to all kinds of alterations, including including extra padding and reordering the frames. 0 Frame have to be preserved. 1 Frame must be discarded. b – File adjust protection This flag tells the tag parser what to do with this body if it's unknown and the file, except for the tag, is altered. This doesn't observe while the audio is completely changed with different audio data. ZERO Body have to be preserved. 1 Frame must be discarded. c – Read only This flag, if set, tells the tool that the contents of this body are intended to be read best. Changing the contents might holiday something, e.g. a signature. If the contents are modified, without wisdom of why the body was once flagged read handiest and without taking the correct means to compensate, e.g. recalculating the signature, the bit need to be cleared. 4.1.2. Body format flags h – Grouping identity This flag indicates whether or no longer this frame belongs in a bunch with other frames. If set, a group identifier byte is delivered to the body. Each body with the same workforce identifier belongs to the similar group. 0 Frame does not include team knowledge 1 Frame comprises workforce data k – Compression This flag indicates whether or not or not the body is compressed. A ‘Information Duration Indicator’ byte have to be integrated in the body. ZERO Body isn't compressed. 1 Body is compressed using zlib zlib deflate approach. If set, this requires the ‘Knowledge Length Indicator’ bit to be set in addition. m – Encryption This flag indicates whether or not or no longer the body is encrypted. If set, one byte indicating with which manner it was once encrypted will probably be introduced to the frame. See description of the ENCR body for additional info about encryption manner registration. Encryption should be performed after compression. Whether or not setting this flag requires the presence of a ‘Data Period Indicator’ is dependent upon the precise set of rules used. ZERO Body isn't encrypted. 1 Body is encrypted. n – Unsynchronisation This flag indicates whether or not or not unsynchronisation was implemented to this frame. See section 6 for details on unsynchronisation. If this flag is set all information from the top of this header to the tip of this frame has been unsynchronised. Even Though fascinating, the presence of a ‘Information Length Indicator’ is not made obligatory by means of unsynchronisation. 0 Frame has now not been unsynchronised. 1 Frame has been unsyrchronised. p – Knowledge duration indicator This flag indicates that a information length indicator has been delivered to the body. the data period indicator is the price one would write because the ‘Frame period’ if all of the body layout flags have been zeroed, represented as a 32 bit synchsafe integer. 0 there's no Knowledge Duration Indicator. 1 A KNOWLEDGE duration Indicator has been added to the body. 5. Tag area The default area of an ID3 tag manager tag is prepended to the audio in order that avid gamers can take pleasure in the tips while the data is streamed. It Is however imaginable to append the tag, or make a prepend/append mixture. When picking where an unembedded tag have to be positioned, the next order of preference need to be thought to be. 1. Prepend the tag. 2. Prepend a tag with all necessary knowledge and upload a 2d tag at the end of the record, earlier than tags from other tagging systems. the primary tag is required to have a ARE TRYING TO FIND body. THREE. Add a tag on the end of the record, earlier than tags from other tagging systems. In case 2 and 3 the tag can simply be appended if no different known tags are present. The advised method to in finding ID3 tag supervisor tags are: 1. search for a prepended tag the use of the development present in section THREE.1. 2. If a SEEK frame used to be discovered, use its values to guide additional looking. THREE. search for a tag footer, scanning from the again of the report. for every new tag that may be discovered, the old tag have to be discarded until the update flag in the extended header (phase 3.2) is set. 6. Unsynchronisation The Only goal of unsynchronisation is to make the ID3 tag supervisor tag as appropriate as conceivable with current tool and hardware. there is little need in ‘unsynchronising’ tags if the document is only to be processed best by ID3 tag supervisor aware software and hardware. Unsynchronisation is purely helpful with tags in MPEG 1/2 layer I, II and III, MPEG 2.FIVE and AAC information. 6.1. The unsynchronisation scheme Each Time a fake synchronisation is located throughout the tag, one zeroed byte is inserted after the primary false synchronisation byte. The format of synchronisations that must be altered by ID3 encoders is as follows: %11111111 111xxxxx and need to be changed with: %11111111 00000000 111xxxxx This has the facet impact that each one $FF 00 mixtures must be altered, so that they is not going to be suffering from the deciphering procedure. Therefore the entire $FF 00 combinations need to get replaced with the $FF 00 00 mixture in the course of the unsynchronisation. to indicate utilization of the unsynchronisation, the unsynchronisation flag in the frame header should be set. This bit have to be set if the frame was altered via the unsynchronisation and WON'T be set if unaltered. If all frames in the tag are unsynchronised the unsynchronisation flag within the tag header need to be set. It MUST NEVER be set if the tag has a frame that is now not unsynchronised. Assume the first byte of the audio to be $FF. The unique case whilst the final byte of the remaining body is $FF and no padding nor footer is used will then introduce a false synchronisation. This can also be solved by means of adding a footer, including padding or unsynchronising the body and add $00 to the end of the body information, therefore including more byte to the frame size than a normal unsynchronisation might. Even If no longer most popular, it is allowed to use the closing way on all frames finishing with $FF. It Is preferred that the tag is either utterly unsynchronised or not unsynchronised in any respect. an absolutely unsynchronised tag has no false synchonisations in it, as outlined above, and doesn't finish with $FF. a fully non-unsynchronised tag comprises no unsynchronised frames, and thus the unsynchronisation flag within the header is cleared. Do endure in thoughts, that if compression or encryption is used, the unsynchronisation scheme should be carried out afterwards. While interpreting an unsynchronised body, the unsynchronisation scheme should be reversed first, encryption and decompression afterwards. 6.2. Synchsafe integers In a few portions of the tag it is inconvenient to make use of the unsychronisation scheme as a result of the size of unsynchronised knowledge is not identified upfront, that is particularly problematical with dimension descriptors. the solution in ID3 tag manager is to make use of synchsafe integers, wherein there can by no means be any fake synchs. Synchsafe integers are integers that stay its best possible bit (bit 7) zeroed, making seven bits out of eight available. Thus a 32 bit synchsafe integer can retailer 28 bits of data. Instance: 255 (%11111111) encoded as a SIXTEEN bit synchsafe integer is 383 (%00000001 01111111).

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