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block_additional_mappings_intro.md

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Block Additional Mapping

Extra data or metadata can be added to each Block using BlockAdditional data. Each BlockAdditional contains a BlockAddID that identifies the kind of data it contains. When the BlockAddID is set to "1" the contents of the BlockAdditional element are define by the Codec Mappings defines; see (#codec-blockadditions). When the BlockAddID is set a value greater than "1", then the contents of the BlockAdditional element are defined by the BlockAdditionalMapping element, within the associated Track element, where the BlockAddID element of BlockAdditional element equals the BlockAddIDValue of the associated Track's BlockAdditionalMapping element. That BlockAdditionalMapping element identifies a particular Block Additional Mapping by the BlockAddIDType.

The following XML depicts a use of a Block Additional Mapping to associate a timecode value with a Block:

<Segment>
  <!--Mandatory elements omitted for readability-->
  <Tracks>
    <TrackEntry>
      <TrackNumber>1</TrackNumber>
      <TrackUID>568001708</TrackUID>
      <TrackType>1</TrackType>
      <BlockAdditionalMapping>
        <BlockAddIDValue>2</BlockAddIDValue><!--arbitrary value
          used in BlockAddID-->
        <BlockAddIDName>timecode</BlockAddIDName>
        <BlockAddIDType>12</BlockAddIDType>
      </BlockAdditionalMapping>
      <CodecID>V_FFV1</CodecID>
      <Video>
        <PixelWidth>1920</PixelWidth>
        <PixelHeight>1080</PixelHeight>
      </Video>
    </TrackEntry>
  </Tracks>
  <Cluster>
    <Timestamp>3000</Timestamp>
    <BlockGroup>
      <Block>{binary video frame}</Block>
      <BlockAdditions>
        <BlockMore>
          <BlockAddID>2</BlockAddID><!--arbitrary value from
            BlockAdditionalMapping-->
          <BlockAdditional>01:00:00:00</BlockAdditional>
        </BlockMore>
      </BlockAdditions>
    </BlockGroup>
  </Cluster>
</Segment>

Block Additional Mappings detail how additional data MAY be stored in the BlockMore element with a BlockAdditionMapping element, within the Track element, which identifies the BlockAdditional content. Block Additional Mappings define the BlockAddIDType value reserved to identify that type of data as well as providing an optional label stored within the BlockAddIDName element. When the Block Additional Mapping is dependent on additional contextual information, then the Mapping SHOULD describe how such additional contextual information is stored within the BlockAddIDExtraData element.