Internet-Draft Matroska Tags July 2023
Lhomme, et al. Expires 3 January 2024 [Page]
Workgroup:
CELLAR Group
Internet-Draft:
draft-ietf-cellar-tags-11
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Lhomme
M. Bunkus
D. Rice

Matroska Media Container Tag Specifications

Abstract

This document defines the Matroska tags, namely the tag names and their respective semantic meaning.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 3 January 2024.

▲

Table of Contents

1. Introduction

Matroska is a multimedia container format. It can store timestamped multimedia data but also chapters and tags. The Tag Elements add important metadata to identify and classify the information found in a Matroska Segment. It can tag a whole Segment, separate Track Elements, individual Chapter elements or Attachment Elements.

While the Matroska tagging framework allows anyone to create their own custom tags, it's important to have a common set of values for interoperability. This document intends to define a set of common tag names used in Matroska.

2. Status of this document

This document is a work-in-progress specification defining the Matroska file format as part of the IETF Cellar working group. It uses basic elements and concept already defined in the Matroska specifications defined by this workgroup [Matroska].

3. Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

4. Tagging

When a Tag is nested within another Tag, the nested Tag becomes an attribute of the base tag. For instance, if you wanted to store the dates that a singer used certain addresses for, that singer being the lead singer for a track that included multiple bands simultaneously, then your tag tree would look something like this:

In this way, it becomes possible to store any Tag as attributes of another tag.

Multiple items SHOULD never be stored as a list in a single TagString. If there is more than one tag of a certain type to be stored, then more than one SimpleTag SHOULD be used.

4.1. Why official tags matter

There is a debate between people who think all tags SHOULD be free and those who think all tags SHOULD be strict. If you look at this page you will realize we are in between.

Advanced-users application might let you put any tag in your file. But for the rest of the applications, they usually give you a basic list of tags you can use. Both have their needs. But it's usually a bad idea to use custom/exotic tags because you will probably be the only person to use this information even though everyone else could benefit from it. So hopefully, when someone wants to put information in one's file, they will find an official one that fit them and hopefully use it ! If it's not in the list, this person can contact us any time for addition of such a missing tag. But it doesn't mean it will be accepted... Matroska files are not meant the become a whole database of people who made costumes for a film. A website would be better for that... It's hard to define what SHOULD be in and what doesn't make sense in a file. So we'll treat each request carefully.

We also need an official list simply for developers to be able to display relevant information in their own design (if they choose to support a list of meta-information they SHOULD know which tag has the wanted meaning so that other apps could understand the same meaning).

4.2. Tag Formatting

  • The TagName SHOULD consists of capital letters, numbers and the underscore character '_'.
  • The TagName SHOULD NOT contain any space.
  • TagNames starting with the underscore character '_' are not official tags; see Section 4.1.
  • The fields with dates SHOULD have the following format: YYYY-MM-DD hh:mm:ss.mss YYYY = Year, MM = Month, DD = Days, HH = Hours, mm = Minutes, ss = Seconds, mss = Milliseconds. To store less accuracy, you remove items starting from the right. To store only the year, you would use, "2004". To store a specific day such as May 1st, 2003, you would use "2003-05-01".
  • Fields that require a Float SHOULD use the "." mark instead of the "," mark. To display it differently for another local, applications SHOULD support auto replacement on display. Also, a thousandths separator SHOULD NOT be used.
  • For currency amounts, there SHOULD only be a numeric value in the Tag. Only numbers, no letters or symbols other than ".". For instance, you would store "15.59" instead of "$15.59USD".

4.3. Target types

The TargetType element allows tagging of different parts that are inside or outside a given file. For example, in an audio file with one song you could have information about the album it comes from and even the CD set even if it's not found in the file.

For application to know what kind of information (like TITLE) relates to a certain level (CD title or track title), we also need a set of official TargetType names. For now audio and video will have different values & names. That also means the same tag name can have different meanings depending on where it is (otherwise, we would end up with 15 TITLE_ tags).

Table 1: TargetTypeValue values semantic description
TargetTypeValue Audio strings Video strings Comment
70 COLLECTION COLLECTION the high hierarchy consisting of many different lower items
60 EDITION / ISSUE / VOLUME / OPUS SEASON / SEQUEL / VOLUME a list of lower levels grouped together
50 ALBUM / OPERA / CONCERT MOVIE / EPISODE / CONCERT the most common grouping level of music and video (equals to an episode for TV series)
40 PART / SESSION PART / SESSION when an album or episode has different logical parts
30 TRACK / SONG CHAPTER the common parts of an album or a movie
20 SUBTRACK / PART / MOVEMENT SCENE corresponds to parts of a track for audio (like a movement)
10 - SHOT the lowest hierarchy found in music or movies

An upper level value tag applies to the lower level. That means if a CD has the same artist for all tracks, you just need to set the ARTIST tag at level 50 (ALBUM) and not to each TRACK (but you can). That also means that, if some parts of the CD have no known ARTIST, the value MUST be set to nothing (a void string "").

When a level doesn't exist it MUST NOT be specified in the files, so that the TOTAL_PARTS and PART_NUMBER elements match the same levels.

Here is an example of how these organizational tags work: If you set 10 TOTAL_PARTS to the ALBUM level (40) it means the album contains 10 lower parts. The lower part in question is the first lower level that is specified in the file. So, if it's TRACK (30), then that means it contains 10 tracks. If it's MOVEMENT (20), that means it's 10 movements, etc.

4.4. Official tags

The following is a complete list of the supported Matroska Tags. While it is possible to use Tag names that are not listed below, this is not recommended as compatibility will be compromised. If you find that there is a Tag missing that you would like to use, then please contact the Matroska team for its inclusion in the specifications before the format reaches 1.0.

4.5. Nesting Information

Nesting Information tags are intended to contain other tags.

Table 2: Nesting Information tags
Tag Name Type Description
ORIGINAL - A special tag that is meant to have other tags inside (using nested tags) to describe the original work of art that this item is based on. All tags in this list can be used "under" the ORIGINAL tag like LYRICIST, PERFORMER, etc.
SAMPLE - A tag that contains other tags to describe a sample used in the targeted item taken from another work of art. All tags in this list can be used "under" the SAMPLE tag like TITLE, ARTIST, DATE_RELEASED, etc.
COUNTRY UTF-8 The name of the country that is meant to have other tags inside (using nested tags) to country specific information about the item, in the Matroska countries form, i.e. [BCP47] two-letter region subtag, without the UK exception. All tags in this list can be used "under" the COUNTRY_SPECIFIC tag like LABEL, PUBLISH_RATING, etc.

4.6. Organization Information

Table 3: Organization Information tags
Tag Name Type Description
TOTAL_PARTS UTF-8 Total number of parts defined at the first lower level. (e.g., if TargetType is ALBUM, the total number of tracks of an audio CD)
PART_NUMBER UTF-8 Number of the current part of the current level. (e.g., if TargetType is TRACK, the track number of an audio CD)
PART_OFFSET UTF-8 A number to add to PART_NUMBER, when the parts at that level don't start at 1. (e.g., if TargetType is TRACK, the track number of the second audio CD)

4.7. Titles

Table 4: Titles tags
Tag Name Type Description
TITLE UTF-8 The title of this item. For example, for music you might label this "Canon in D", or for video's audio track you might use "English 5.1" This is akin to the "TIT2" tag in [ID3v2].
SUBTITLE UTF-8 Sub Title of the entity.

4.8. Nested Information

Nested Information includes tags contained in other tags.

Table 5: Nested Information tags
Tag Name Type Description
URL UTF-8 URL corresponding to the tag it's included in.
SORT_WITH UTF-8 A child element to indicate what alternative value the parent tag can have to be sorted -- for example, "Pet Shop Boys" instead of "The Pet Shop Boys". Or "Marley Bob" and "Marley Ziggy" (no comma needed).
INSTRUMENTS UTF-8 The instruments that are being used/played, separated by a comma. It SHOULD be a child of the following tags: ARTIST, LEAD_PERFORMER, or ACCOMPANIMENT.
EMAIL UTF-8 Email corresponding to the tag it's included in.
ADDRESS UTF-8 The physical address of the entity. The address SHOULD include a country code. It can be useful for a recording label.
FAX UTF-8 The fax number corresponding to the tag it's included in. It can be useful for a recording label.
PHONE UTF-8 The phone number corresponding to the tag it's included in. It can be useful for a recording label.

4.9. Entities

Table 6: Entities tags
Tag Name Type Description
ARTIST UTF-8 A person or band/collective generally considered responsible for the work. This is akin to the "TPE1" tag in [ID3v2].
LEAD_PERFORMER UTF-8 Lead Performer/Soloist(s). This can sometimes be the same as ARTIST.
ACCOMPANIMENT UTF-8 Band/orchestra/accompaniment/musician. This is akin to the "TPE2" tag in [ID3v2].
COMPOSER UTF-8 The name of the composer of this item. This is akin to the "TCOM" tag in [ID3v2].
ARRANGER UTF-8 The person who arranged the piece, e.g., Ravel.
LYRICS UTF-8 The lyrics corresponding to a song (in case audio synchronization is not known or as a doublon to a subtitle track). Editing this value, when subtitles are found, SHOULD also result in editing the subtitle track for more consistency.
LYRICIST UTF-8 The person who wrote the lyrics for a musical item. This is akin to the "TEXT" tag in [ID3v2].
CONDUCTOR UTF-8 Conductor/performer refinement. This is akin to the "TPE3" tag in [ID3v2].
DIRECTOR UTF-8 This is akin to the "IART" tag [RIFF.tags].
ASSISTANT_DIRECTOR UTF-8 The name of the assistant director.
DIRECTOR_OF_PHOTOGRAPHY UTF-8 The name of the director of photography, also known as cinematographer. This is akin to the "ICNM" tag in [RIFF.tags].
SOUND_ENGINEER UTF-8 The name of the sound engineer or sound recordist.
ART_DIRECTOR UTF-8 The person who oversees the artists and craftspeople who build the sets.
PRODUCTION_DESIGNER UTF-8 Artist responsible for designing the overall visual appearance of a movie.
CHOREGRAPHER UTF-8 The name of the choregrapher
COSTUME_DESIGNER UTF-8 The name of the costume designer
ACTOR UTF-8 An actor or actress playing a role in this movie. This is the person's real name, not the character's name the person is playing.
CHARACTER UTF-8 The name of the character an actor or actress plays in this movie. This SHOULD be a sub-tag of an ACTOR tag in order not to cause ambiguities.
WRITTEN_BY UTF-8 The author of the story or script (used for movies and TV shows).
SCREENPLAY_BY UTF-8 The author of the screenplay or scenario (used for movies and TV shows).
EDITED_BY UTF-8 This is akin to the "IEDT" tag in [RIFF.tags].
PRODUCER UTF-8 Produced by. This is akin to the "IPRO" tag in [RIFF.tags].
COPRODUCER UTF-8 The name of a co-producer.
EXECUTIVE_PRODUCER UTF-8 The name of an executive producer.
DISTRIBUTED_BY UTF-8 This is akin to the "IDST" tag in [RIFF.tags].
MASTERED_BY UTF-8 The engineer who mastered the content for a physical medium or for digital distribution.
ENCODED_BY UTF-8 This is akin to the "TENC" tag in [ID3v2].
MIXED_BY UTF-8 DJ mix by the artist specified
REMIXED_BY UTF-8 Interpreted, remixed, or otherwise modified by. This is akin to the "TPE4" tag in [ID3v2].
PRODUCTION_STUDIO UTF-8 This is akin to the "ISTD" tag in [RIFF.tags].
THANKS_TO UTF-8 A very general tag for everyone else that wants to be listed.
PUBLISHER UTF-8 This is akin to the "TPUB" tag in [ID3v2].
LABEL UTF-8 The record label or imprint on the disc.

4.10. Search and Classification

Table 7: Search and Classification tags
Tag Name Type Description
GENRE UTF-8 The main genre (classical, ambient-house, synthpop, sci-fi, drama, etc.). The format follows the infamous "TCON" tag in [ID3v2].
MOOD UTF-8 Intended to reflect the mood of the item with a few keywords, e.g., "Romantic", "Sad" or "Uplifting". The format follows that of the "TMOO" tag in [ID3v2].
ORIGINAL_MEDIA_TYPE UTF-8 Describes the original type of the media, such as, "DVD", "CD", "computer image," "drawing," "lithograph," and so forth. This is akin to the "TMED" tag in [ID3v2].
CONTENT_TYPE UTF-8 The type of the item. e.g., Documentary, Feature Film, Cartoon, Music Video, Music, Sound FX, ...
SUBJECT UTF-8 Describes the topic of the file, such as "Aerial view of Seattle."
DESCRIPTION UTF-8 A short description of the content, such as "Two birds flying."
KEYWORDS UTF-8 Keywords to the item separated by a comma, used for searching.
SUMMARY UTF-8 A plot outline or a summary of the story.
SYNOPSIS UTF-8 A description of the story line of the item.
INITIAL_KEY UTF-8 The initial key that a musical track starts in. The format is identical to "TKEY" tag in [ID3v2].
PERIOD UTF-8 Describes the period that the piece is from or about. For example, "Renaissance".
LAW_RATING UTF-8 Depending on the COUNTRY it's the format of the rating of a movie (P, R, X in the USA, an age in other countries or a URI defining a logo).

4.11. Temporal Information

Table 8: Temporal Information tags
Tag Name Type Description
DATE_RELEASED UTF-8 The time that the item was originally released. This is akin to the "TDRL" tag in [ID3v2].
DATE_RECORDED UTF-8 The time that the recording began. This is akin to the "TDRC" tag in [ID3v2].
DATE_ENCODED UTF-8 The time that the encoding of this item was completed began. This is akin to the "TDEN" tag in [ID3v2].
DATE_TAGGED UTF-8 The time that the tags were done for this item. This is akin to the "TDTG" tag in [ID3v2].
DATE_DIGITIZED UTF-8 The time that the item was transferred to a digital medium. This is akin to the "IDIT" tag in [RIFF.tags].
DATE_WRITTEN UTF-8 The time that the writing of the music/script began.
DATE_PURCHASED UTF-8 Information on when the file was purchased; see also Section 4.16 on purchase tags.

4.12. Spatial Information

Table 9: Spatial Information tags
Tag Name Type Description
RECORDING_LOCATION UTF-8 The location where the item was recorded, in the Matroska countries form, i.e. [BCP47] two-letter region subtag, without the UK exception. This code is followed by a comma, then more detailed information such as state/province, another comma, and then city. For example, "US, Texas, Austin". This will allow for easy sorting. It is okay to only store the country, or the country and the state/province. More detailed information can be added after the city through the use of additional commas. In cases where the province/state is unknown, but you want to store the city, simply leave a space between the two commas. For example, "US, , Austin".
COMPOSITION_LOCATION UTF-8 Location that the item was originally designed/written, in the Matroska countries form, i.e. [BCP47] two-letter region subtag, without the UK exception. This code is followed by a comma, then more detailed information such as state/province, another comma, and then city. For example, "US, Texas, Austin". This will allow for easy sorting. It is okay to only store the country, or the country and the state/province. More detailed information can be added after the city through the use of additional commas. In cases where the province/state is unknown, but you want to store the city, simply leave a space between the two commas. For example, "US, , Austin".
COMPOSER_NATIONALITY UTF-8 Nationality of the main composer of the item, mostly for classical music, in the Matroska countries form, i.e. [BCP47] two-letter region subtag, without the UK exception.

4.13. Personal

Table 10: Personal tags
Tag Name Type Description
COMMENT UTF-8 Any comment related to the content.
PLAY_COUNTER UTF-8 The number of time the item has been played.
RATING UTF-8 A numeric value defining how much a person likes the song/movie. The number is between 0 and 5 with decimal values possible (e.g., 2.7), 5(.0) being the highest possible rating. Other rating systems with different ranges will have to be scaled.

4.14. Technical Information

Table 11: Technical Information tags
Tag Name Type Description
ENCODER UTF-8 The software or hardware used to encode this item. ("LAME" or "XviD")
ENCODER_SETTINGS UTF-8 A list of the settings used for encoding this item. No specific format.
BPS UTF-8 The average bits per second of the specified item. This is only the data in the Blocks, and excludes headers and any container overhead.
FPS UTF-8 The average frames per second of the specified item. This is typically the average number of Blocks per second. In the event that lacing is used, each laced chunk is to be counted as a separate frame.
BPM UTF-8 Average number of beats per minute in the complete target (e.g., a chapter). Usually a decimal number.
MEASURE UTF-8 In music, a measure is a unit of time in Western music like "4/4". It represents a regular grouping of beats, a meter, as indicated in musical notation by the time signature. The majority of the contemporary rock and pop music you hear on the radio these days is written in the 4/4 time signature.
TUNING UTF-8 It is saved as a frequency in hertz to allow near-perfect tuning of instruments to the same tone as the musical piece (e.g., "441.34" in Hertz). The default value is 440.0 Hz.
REPLAYGAIN_GAIN binary The gain to apply to reach 89dB SPL on playback. This is based on the [ReplayGain] standard. Note that ReplayGain information can be found at all TargetType levels (track, album, etc).
REPLAYGAIN_PEAK binary The maximum absolute peak value of the item. This is based on the [ReplayGain] standard.

4.15. Identifiers

Table 12: Identifiers tags
Tag Name Type Description
ISRC UTF-8 The International Standard Recording Code [ISRC], excluding the "ISRC" prefix and including hyphens.
MCDI binary This is a binary dump of the TOC of the CDROM that this item was taken from. This holds the same information as the "MCDI" in [ID3v2].
ISBN UTF-8 International Standard Book Number [ISBN].
BARCODE UTF-8 European Article Numbering EAN-13 barcode defined in [GS1] General Specifications.
CATALOG_NUMBER UTF-8 A label-specific string used to identify the release -- for example, TIC 01.
LABEL_CODE UTF-8 A 4-digit or 5-digit number to identify the record label, typically printed as (LC) xxxx or (LC) 0xxxx on CDs medias or covers (only the number is stored).
LCCN UTF-8 Library of Congress Control Number [LCCN].
IMDB UTF-8 Internet Movie Database [IMDb] identifier. "tt" followed by at least 7 digits for Movies, TV Shows, and Episodes.
TMDB UTF-8 The Movie DB "movie_id" or "tv_id" identifier for movies/TV shows [MovieDB]. The variable length digits string MUST be prefixed with either "movie/" or "tv/".
TVDB UTF-8 The TV Database "Series ID" or "Episode ID" identifier for TV shows [TheTVDB]. Variable length all-digits string identifying a TV Show.
TVDB2 UTF-8 The TV Database [TheTVDB] tag which can include movies. The variable length digits string representing a "Series ID", "Episode ID" or "Movie ID" identifier MUST be prefixed with "series/", "episodes/" or "movies/" respectively.

4.16. Commercial

Table 13: Commercial tags
Tag Name Type Description
PURCHASE_ITEM UTF-8 URL to purchase this file. This is akin to the "WPAY" tag in [ID3v2].
PURCHASE_INFO UTF-8 Information on where to purchase this album. This is akin to the "WCOM" tag in [ID3v2].
PURCHASE_OWNER UTF-8 Information on the person who purchased the file. This is akin to the "TOWN" tag in [ID3v2].
PURCHASE_PRICE UTF-8 The amount paid for entity. There SHOULD only be a numeric value in here. Only numbers, no letters or symbols other than ".". For instance, you would store "15.59" instead of "$15.59USD".
PURCHASE_CURRENCY UTF-8 The currency type used to pay for the entity. Use [ISO4217] for the 3 letter alphabetic code.

4.18. Notes

  • In the Target list, a logical OR is applied on all tracks, a logical OR is applied on all chapters. Then a logical AND is applied between the Tracks list and the Chapters list to know if an element belongs to this Target.

5. Security Considerations

Tag values can be either strings or binary blobs. This document inherits security considerations from the EBML and Matroska documents.

6. IANA Considerations

To be determined.

7. Normative References

[BCP47]
Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, , <https://www.rfc-editor.org/info/rfc5646>.
[GS1]
"GS1 General Specifications", GS1 20.0, , <https://www.gs1.org/standards/barcodes-epcrfid-id-keys/gs1-general-specifications>.
[ID3v2]
Nilsson, M., Mahoney, D., Ed., and J. Sundstrom, Ed., "ID3 tag version 2.3.0", , <https://id3.org/id3v2.3.0>.
[IMDb]
Internet Movie Database, "IMDb API Documentation", <https://imdb-api.com/api>.
[ISBN]
International ISBN Agency, "ISBN Users' Manual", , <https://www.isbn-international.org/content/isbn-users-manual>.
[ISO4217]
International Organization for Standardization, "ISO 4217 Currency codes", ISO 4217:2015, , <https://www.iso.org/iso-4217-currency-codes.html>.
[ISRC]
IFPI Secretariat, "International Standard Recording Code (ISRC) Handbook", IFPI 3rd Edition, , <https://www.ifpi.org/wp-content/uploads/2020/08/ISRC_Handbook.pdf>.
[LCCN]
United States Library Of Congress, "Library Of Congress Control Number", , <https://www.loc.gov/marc/lccn.html>.
[Matroska]
Lhomme, S., Bunkus, M., and D. Rice, "Media Container Specifications", Work in Progress, Internet-Draft, draft-ietf-cellar-matroska-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-cellar-matroska-10>.
[MovieDB]
The Movie Database, "The Movie Database API", <https://developers.themoviedb.org/3/movies/get-movie-details>.
[ReplayGain]
Robinson, D., "ReplayGain 1.0 specification", , <http://wiki.hydrogenaud.io/index.php?title=Replay_Gain_specification>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[TheTVDB]
The TVDB, "API documentation", <https://www.thetvdb.com/api-information>.

8. Informative References

[RIFF.tags]
Exiftool, "RIFF Tags", <https://exiftool.org/TagNames/RIFF.html>.

Authors' Addresses

Steve Lhomme
Moritz Bunkus
Dave Rice