SMPTE EG 42-2015 Material Exchange Format (MXF) - MXF Descriptive Metadata.pdf

1、 Copyright 2015 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved August 30, 2015 Table of Contents Page Foreword . 2 Introduction 2 1 Scope . 4 2 References . 4 3 Glossary of Acronyms, Terms and Data Types . 4 4 Relating Descri

2、ptive Metadata to Essence 5 5 Metadata Coding 9 6 Guide for Implementing Descriptive Metadata Schemes in MXF 11 7 Operational Considerations 12 Annex A Descriptive Metadata Characteristics (Informative) 13 Annex B Metadata Modeling (Informative). 17 Annex C XML-Schema Implementation (Informative) .

3、24 Annex D Bibliography (Informative) 26 Page 1 of 26 pages SMPTE EG 42:2015 Revision of EG 42-2004 SMPTE ENGINEERING GUIDELINE Material Exchange Format (MXF) MXF Descriptive Metadata SMPTE EG 42:2015 Page 2 of 26 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an in

4、ternationally-recognized standards developing organization. Headquartered and incorporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering Documents, including Standards, Recommended Practices and Engineering Guidelines, are prepared by S

5、MPTEs Technology Committees. Participation in these Committees is open to all with a bona fide interest in their work. SMPTE cooperates closely with other standards-developing organizations, including ISO, IEC and ITU. SMPTE Engineering Documents are drafted in accordance with the rules given in its

6、 Standards Operations Manual. SMPTE EG 42 was prepared by Technology Committee 31FS. Introduction This guideline is entirely informative and intended to provide guidance for implementing descriptive metadata within the header metadata of an MXF file SMPTE ST 377-1. This guideline supplements the MXF

7、 Engineering Guideline SMPTE EG 377-3. This guideline is divided into a number of core sections, each section describing a particular aspect of descriptive metadata. The sections (together with their section number) are as follows: This introduction including the usage of descriptive metadata and us

8、er requirements for descriptive metadata. Section 4: The mechanisms by which descriptive metadata in the MXF header metadata can be linked to the essence in the MXF essence container. Section 5: How to implement descriptive metadata as a sequence of KLV packets in the MXF header metadata and as XML

9、for text-based interfacing. Section 6: Guidance for implementing both MXF descriptive metadata and non-MXF descriptive metadata. Section 7: Considerations for handling descriptive metadata in special operational circumstances. Annex A: Provides a discussion of metadata characteristics. Annex B: Prov

10、ides an introduction to data modeling techniques. Annex C: Provides an example of the options for XML coding. Annex D: Bibliography Dimensions of Descriptive Metadata Use In general terms, the use of descriptive metadata has many dimensions as follows: 1. It is in widespread use within different con

11、tent-based industries, including broadcast, film, music and web authoring. 2. It is in widespread use within different content-based applications, including capture/creation, production, post-production and archive/libraries. SMPTE EG 42:2015 Page 3 of 26 pages 3. It can be divided into several diff

12、erent broad categories including business transactions, publication information, content identification and labeling, compositional information and formatting, etc. 4. It can have different states such as being static for a defined duration, being dynamic (with several kinds of dynamic states includ

13、ing transitory, metronomic, incrementing and so on). 5. It can have different levels of stability with elements having durable values that remain stable or transient values that frequently change. In the header metadata of an MXF file, the metadata is persisted and can be distributed over many copie

14、s. Thus descriptive metadata in an MXF file ought to include only that metadata which can be considered copy persistent. This does not mean that a value can never change between copies, but that, once written, individual copies will have to be edited where changes are required. For some types of met

15、adata, this is not only acceptable, but encouraged, e.g. a property that defines the number of copies made. One of the primary aims of this document is to identify that metadata which can be used to enhance the description of the content in a file. Metadata that is appropriate for use in databases i

16、s not considered in this guideline. Annex A describes metadata characteristics that can aid the reader to understand the attributes of different kinds of metadata items. User Requirements for Descriptive Metadata Many major content production facilities have custom methods for handling the descripti

17、ve metadata associated with the content. As audio-visual content exchange moves from tape-based to file-based operations, the opportunity arises to be able to both embed descriptive metadata in the file and to provide an intimate relationship between the metadata and the audio-visual content. This p

18、rocess allows metadata to be accrued within a file as it passes between operations in a way that has rarely before been achieved. Many users see the ability to embed metadata into an MXF file as a key requirement that extends the use of MXF beyond that primarily for the simple exchange of audio-visu

19、al content. SMPTE EG 42:2015 Page 4 of 26 pages 1 Scope The MXF standard SMPTE ST 377-1 provides for descriptive metadata schemes as “plug-ins” to the MXF header metadata. This guideline is intended to provide guidance for the use of MXF descriptive metadata schemes. This guideline is a supplement t

20、o SMPTE EG 377-3. This guideline explains the common structural metadata components by which all MXF descriptive metadata schemes can be related to the essence they describe. Additional constraints required for MXF descriptive metadata schemes are also described. This guideline describes how MXF des

21、criptive metadata is related to the essence using the structural metadata defined in SMPTE ST 377-1. It also describes how MXF descriptive metadata is coded as KLV data for use in MXF files and as XML for text-based metadata exchange. This guideline also provides guidance for implementing MXF descri

22、ptive metadata schemes. Descriptive metadata is a complex topic and requires at least some basic understandings of the various attributes of descriptive metadata together with data modeling techniques. This guideline provides annexes that summarize these topics. 2 References Note: All references in

23、this document to other SMPTE documents use the current numbering style (e.g. SMPTE ST 336:2007) although, during a transitional phase, the document as published (printed or PDF) may bear an older designation (such as SMPTE 336M-2007). Documents with the same root number (e.g. 336) and publication ye

24、ar (e.g. 2007) are functionally identical. The following documents contain information used in this guideline. At the time of publication, the editions indicated were valid. All standards are subject to revision, and readers of this guideline are encouraged to investigate the possibility of applying

25、 the most recent edition of the documents indicated below. SMPTE ST 298:2009, Universal Labels for Unique Identification of Digital Data SMPTE ST 336:2007, Data Encoding Protocol Using Key-Length-Value SMPTE ST 377-1:2011, Material Exchange Format (MXF) File Format Specification Amendment 1:2012 to

26、SMPTE ST 377-1:2011 Amendment 2:2012 to SMPTE ST 377-1:2011 SMPTE ST 400:2012, SMPTE Labels Structure SMPTE EG 377-3:2013, Material Exchange Format (MXF) Engineering Guideline 3 Glossary of Acronyms, Terms and Data Types The full glossary of acronyms, terms and data types used in the MXF specificati

27、on is given in the MXF file format specification. It is not repeated here to avoid any divergence of meaning. 3.1 Acronyms DM: Descriptive Metadata DMS: Descriptive Metadata Scheme HTML: Hyper-text Markup Language MXF: Material exchange Format SMPTE EG 42:2015 Page 5 of 26 pages O-O: Object Oriented

28、 UML: Unified Modeling Language XML: eXtensible Markup Language (text-based data coding) 3.2 Terms Element: An atomic constituent of a data model. Property: A named value denoting the characteristics of an element. 4 Relating Descriptive Metadata to Essence The MXF structural header metadata describ

29、es the audio-visual content divided into individual essence tracks. Thus each track has associated with it a descriptor of the essence, where each property of that descriptor is static for that track duration. In MXF, each track can be divided into one or more segments, where each segment comprises

30、a link to the appropriate segment of essence in the MXF essence container. This applies whether or not the essence is embedded in the file body. The same principles also apply to descriptive metadata tracks. The MXF format specification SMPTE ST 377-1 defines the descriptive metadata plug-in mechani

31、sm together with the generic set keys for descriptive metadata sets (including any abstract sets) and a generic universal label for identification of a given DM scheme. It also includes a standardized mechanism to link descriptive metadata to any individual essence track, a defined group of essence

32、tracks or all the essence tracks. This mechanism also defines the start and stop points along the essence track(s) where the descriptive metadata applies. 4.1 MXF Descriptive Metadata SMPTE ST 377-1 defines DM tracks to describe the content of the essence in the essence container. Additional objects

33、 include a “DM segment” that defines a descriptive metadata track that can be used to describe the essence tracks and a “DM source clip” that can be used to link to either a real metadata track in the essence container or to a descriptive metadata track in the header metadata. Note: Examples of a me

34、tadata track within the essence container are defined in the system item of the SDTI-CP specifications SMPTE ST 326 and SMPTE ST 331. 4.2 DM Tracks Descriptive metadata tracks can be timeline, event or static. SMPTE ST 377-1 defines the use of these track types for descriptive metadata, which is sum

35、marized in the following sub-sections: 4.2.1 Timeline track There can be multiple DM segments on a timeline track and the sum of the segments will equal the total track length. Thus adjacent segments of descriptive metadata will be butt-joined together and leave no gaps. It is perfectly valid to hav

36、e a timeline track with a single DM segment, which occupies the whole track duration. A timeline descriptive metadata track would be used to support metadata that is effectively timed along the track in a piecewise linear manner. 4.2.2 Event track There can be multiple DM segments on an event track

37、and the segments are unconstrained along the time axis. Thus adjacent segments can overlap or they can leave gaps where no descriptive metadata applies. SMPTE EG 42:2015 Page 6 of 26 pages This kind of descriptive metadata track allows the greatest flexibility (and hence the greatest complexity) as

38、illustrated in Figure 1. 4.2.3 Static track If the DM track is a static type, then it has no timeline and all DM segments apply descriptive metadata to the entire duration of the linked essence track(s). There can be multiple DM segments that link to different essence tracks, but all DM segments in

39、a static track describe the contents of the entire track duration. This is a special case of using descriptive metadata and applies to those kinds of descriptive metadata that have an inherently static value for the duration of the essence. Descriptive metadata on a static track cannot be accessed d

40、irectly if the essence has a timeline. In this case, the material package would access the static descriptive metadata in a source package using a DM source clip on a timeline or event track. This is analogous to sourcing a JPEG still image on a static track in a source package from a timeline track

41、 in the material package. Accessing metadata tracks through the DM source clip mechanism is explained in the next section. If the descriptive metadata describes a static essence element such as a coded still picture (e.g. JPEG), then a static track would be used. 4.3 Using DM Segments MXF provides f

42、or metadata tracks that logically run in parallel with the essence tracks. In effect, this adds tracks where metadata can be defined that links to one or more frames of one or more essence tracks. Note that MXF uses the same concept for the time-code track with the constraint that the time-code trac

43、k always defines the time for all the other essence tracks. Figure 1 Descriptive metadata track segments and their relationship to the content of an MXF essence container Figure 1 illustrates that DM segment 1 is linking the metadata framework(s) of this segment to all the essence tracks of the firs

44、t part of the A/V content (excluding the time-code track). DM segment 2 is linking the metadata framework(s) of this segment to only the middle part of the sound tracks. DM segment 3 is linking the metadata framework(s) to only the last part of the picture track (excluding the time-code track). T i

45、me co d e T ra ck Pi ct u re T ra ck Vi rt u a l D M T ra ck So u n d T ra ck 2 So u n d T ra ck 1 R o o t Se t s (Pre f a ce , I d e n t perhaps as a result of file editing or other operations that mix essence tracks in a file. Such files can end up with a mixture of different DM schemes. To avoid

46、decoder confusion or worse, encoders need to ensure that each DM track is unique to each DM framework in a file, thereby ensuring that each DM track contains the contents from one DM framework only. Collating different DM schemes onto the same DM tracks in a file could cause decoder confusion, a fai

47、lure to respond to one of the schemes or worse. If an editing operation combines essence tracks from two or more sources, then the associated DM tracks might also need to be combined. In such a case, the combining process will depend on the nature of the DM SMPTE EG 42:2015 Page 9 of 26 pages track.

48、 For example DM on a static track has DM values that are static, but they apply only to the relevant source essence track. Whether such values can be used to create a new DM track for the new static track is dependent on the metadata characteristic. In many cases, human intervention will be required

49、 to create new metadata values. For example, mixing a track named “MyTrack15” with another track named “MyTrack31” will create new material and need human intervention to create the new metadata values. Other metadata such as Picture Format might well have the same values and can thus be automatically transferred to the new DM track. A full analysis of the operations needed to mix different descriptive metadata sources is specialist in nature and beyond the scope of this guideline. 5 Metadata Coding The data structures considered in the previous section nee