KLV : Key: The Type Identifier (or Universal Label)

The normalization of the key is defined in the SMPTE 298 : Universal Labels (UL) for Unique Identification of Digital Data document.

In summary, it's a unique key for each type of KLV but not unique for each KLV. We can have the same key multiple times in a MXF file. A perfect example is the KLV for the frame: the same key for each KLV that contains a frame.

A Universal Label (UL) follows a specific format : 

Hexa Format   =  060e2b34020501010d01020101020400
SMPTE Format  =  060e2b34.02050101.0d010201.01020400

They exist a lot of Universal Label, here are a few examples below:

Key / Universal Label (UL) KLV Type
060e2b34.02050101.0d010201.01020400 Partition Pack - Header
060e2b34.02050101.0d010201.01030400 Partition Pack - Body
060e2b34.02050101.0d010201.01040400 Partition Pack - Footer
060e2b34.02050101.0d010201.01050100 Primer Pack
060e2b34.02530101.0d010101.01013000 Identification
060e2b34.02530101.0d010101.01013600 Material Package
060e2b34.02530101.0d010101.01010f00 Sequence
060e2b34.02530101.0d010101.01011100 Source Clip
060e2b34.02050101.0d010201.01110100 Random Index Pack
060e2b34.02040107.0d010301.027e0100 Encrypted Essence
060e2b34.01020101.0d010301.15010801 Picture Essence
...

As we can see, each Universal Label (UL) identifies a type of KLV.

We can notice that the header (060e2b34) is always identical. After that, depending on the type of the KLV, some changes occur :-)

After the header (060e2b34), all octets are importants because they act like parameters, options, or status for the KLV. For example, the Partition Packs have many identifiers with a common base. Their parameters determine whether it's a Header, a Body or a Footer, and wheter they are complete or incomplete, open or closed, etc.

We can take our example of Partition Packs and highlight the difference :

Universal Label (UL) Type
060e2b34.02050101.0d010201.01020400 Partition Pack - Header
060e2b34.02050101.0d010201.01030400 Partition Pack - Body
060e2b34.02050101.0d010201.01040400 Partition Pack - Footer

In the case of Partition Pack, we observe that only the second-to-last octets change (in bold), they respectively represent :

The value just after (04) determines the status of the Partition Pack : With the value 04, the Partition Pack is considered Closed & Complete

Each KLV has its own specific characteristics: it will be necessary to read each SMPTE document to understand and collect these precious parameters, and thus identify Universal Labels for each type of KLV (they’re like Pokémons).

You can also get a list of multiple Universal Labels from the following registries, but they won’t tell you what each octet corresponds to :

We will see in detail how a Universal Label (UL) is composed, inside a key. Note that knowing all of this is not essential and won't stop you from interpreting data in the Value field. It's just a bonus to your knowledge.

Inside of Key

As we can see, after the key header (060e2b34), each octet has its own characteristics.

Here is a schematic representation of the inside of the K in a KLV :

MXF key

The size of the Universal Label (UL) is 16 octets and it is subdivisible into three main part :

The following table provides a quick overview of the different parts of the key :

UL Header UL Designators Item Designator
2 octets 6 octets 8 octets
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Object ID UL Size UL Code SMPTE Designator Category Designator Registry Designator Structure Designator Version Number #1 #2 #3 #4 #5 #6 #7 #8
Signature
0x06 0x0E 0x2B 0x34
4 octets

As standardized, the first four octets always start with the hexadecimal sequence: 0x06,0x0e, 0x2b,0x34. That is its signature. And this allows us to quickly identify these KLVs 1.

If you take a look at the UL Header (first two octets) : we have Object ID + UL Size which have a format that will look familiar. We start with an identifier, then a size, and finally other data... Yes, that's indeed the KLV format, which also structures the inside of the key :-)

Thus, the second octet (UL Size) indicates the size of the Key's data : 0x0E represents 14 octets, which correspond to the following octets, from SMPTE Designator to the last Item Designator #8

Here is a descriptive table of each octet in Universal Label (UL) :

N° Name of the field Description Data
1 Object ID Its identifier 0x06 UL Header
2 UL Size Remaining size of the key 0x0E UL Header
3 UL Code Subidentifier ISO + ORG 0x2B UL Designator
4 SMPTE Designator Subidentifier SMPTE 0x34 UL Designator
5 Category Designator Data Type 0x01-0x7E UL Designator
6 Registry Designator Universal Sets 0x?? UL Designator
7 Structure Designator 0x?? UL Designator
8 Version Number Registry version 0x?? UL Designator
9-16 Universal-Set Designator Parameters & Options .... Item Designator

Category Designator

Category Designator allows us to quickly identify the type of data contained in the Value part. To be brief about the main categories :

Here is an overview table of the different Category Designator (5) accompanied by the next Registry Designator (6), which allows for more precision about the type of data (in green, the main elements in an MXF from a DCP) :

Category Designator (5) Registry Designator (6)
Dictionnaries0x01Raw data
0x010x01Metadata Dictionary
0x010x02Essence Dictionary
0x010x03Control Dictionary
0x010x04Types Dictionary
Groups (Sets or Packs)0x02Structured data
0x020x01Universal Set
0x020x02Global Set
0x020x03Local Set
0x020x13Local Set
0x020x53Local Set
0x020x04Variable Length Pack
0x020x05Defined Length Pack
0x020x06Reserved / Forbidden
Wrappers & Containers0x03
0x030x01Simple Wrapper & Container
0x030x02Complex Wrapper & Container
SMPTE Labels0x04Not used as KLV key
Registered Private Information 0x05
Reserved0x06
......
Reserved0x7E

Registry Designator

Registry Designator identifies the specific registry within a specific category. (for example, Essence Dictionary which is a subcategory of "Dictionaries"). See the table above for the different Registry Designator.

You may have noticed the presence of several Local Sets with three different Registry Designator. By default in the KLV standards (2004), Local Set has a Registry Designator code of 0x03. In the MXF standards (2011), the different types of KLV that comply with Local Sets have the Registry Designator codes of 0x53 or 0x13.

Why are there these different Registry Designator for the Local Set ? We won’t spend too much time on this because we’ll cover it in the MXF chapter MXF : KLV : Values - Local Sets along with the notes 2, but to quickly summarize, this will have an impact on the data stored in the Value part. Only the last Local Set 0x53 is useful for us : it's the Registry Designator for the KLV types in the MXF DCP.

Note that we have the same behavior with the Registry Designator for Variable-Length Pack, but we only have one Registry Designator set to 0x04 3

Structure Designator

Structure Designator identifies the variant within the Registry Designator. According to the standard, it uses as a pseudo major version number ("Major number"), ranging from 0x01 to 0x7F. Most of the time, this value is 0x01.

Version Number

Version Number gives the version of Item Designator (the following octets)

Item Designator

Item Designator (or Universal-Set Designator) is the unique identifier for this item within its category. It's on the last 8 octets 4 of our Universal Label. We will look at this in more detail in the chapter "KLV Types".

Conclusion

Let's take a last look at this diagram of the Key :

MXF key

Now that you know all of this, you can put it away somewhere.

Except for knowing what the Category and Registry correspond to in order to quickly identify the data type, this will have little — if any — impact on how you handle the data. These essential details will be available in each standard describing the data structure and how to process it :)

Keep in mind that an identifier = Universal Label (UL) = a type of data.

Now let's look at the chapter KLV Length.

Notes

  1. We will see later that there are main KLVs, called Universal Sets and sub-KLVs - stored within the Value part - called Local Sets ↩

  2. Length is variable, from 1 octet to 4 octets, but in our case, it's only 2 octets. This is determined by the value of the Registry Designator. If you remember, we had several Local Set with different Registry Designator values, such as 0x03, 0x13 and 0x53. ↩

    However, this is only a tiny fraction of the possible values. In the documentation, there are many more. Each value represents a Local Tag size and a Length size for the item.

    In MXF DCP, we have only the value 0x53, which corresponds to a Length size and a Local Tag size of 2 octets (16 bits) each.

    To your information, Here is a descriptive table of the different values of Registry Designator for the other Local Set. Only the green will be useful (We won't see the others) :

    First 6 octets
    of Universal Label    		 Registry Designator
    (position 6)    		 Size of
    Local Tag    		 Size of
    Length    		 Informations
    060e2b34.0203 0x03 1 octet BER short/long Any size
    060e2b34.020b 0x0b BER OID BER short/long Any size
    060e2b34.0213 0x13 2 octets BER short/long Any size
    060e2b34.021b 0x1b 4 octets BER short/long Any size
    060e2b34.0223 0x23 1 octet 1 octet Size up to 255
    060e2b34.022b 0x2b BER OID 1 octet Size up to 255
    060e2b34.0233 0x33 2 octets 1 octet Size up to 255
    060e2b34.023b 0x3b 4 octets 1 octet Size up to 255
    060e2b34.0243 0x43 1 octet 2 octets Size up to 65535
    060e2b34.024b 0x4b BER OID 2 octets Size up to 65535
    060e2b34.0253 0x53 2 octets 2 octets Size up to 65535
    060e2b34.025b 0x5b 4 octets 2 octets Size up to 65535
    060e2b34.0263 0x63 1 octet 4 octets Size up to ( 232 )-1 (4.294.967.295)
    060e2b34.026b 0x6b BER OID 4 octets Size up to ( 232 )-1
    060e2b34.0273 0x73 2 octets 4 octets Size up to ( 232 )-1
    060e2b34.027b 0x7b 4 octets 4 octets Size up to ( 232 )-1

  3. Length is variable, from 1 octet to 4 octets, but in our case, it's a BER encoding. This is determined by the value of the Registry Designator. ↩

    For your information, here is a descriptive table of the different values of Registry Designator for the other Variable-Length Pack. Only the green will be useful (We won't see the others)

    first 6 octets
    Universal Label    		 Registry
    Designator
    (6)    		 Size
    Length    		 Informations
    060e2b34.0204 0x04 BER short/long Any size
    060e2b34.0224 0x24 1 octet Size up to 255
    060e2b34.0244 0x44 2 octets Size up to 65535
    060e2b34.0264 0x64 4 octets Size up to (232 - 1)

  4. The standard is naughty, it indicates that the size of Item Designator may be from 1 octet to 8 octets. If that's the case, it will be padded with zeros to make... 8 octets. To sum up, Item Designator is always 8 octets long.  ↩