Vidispine supports adding subtitles to an item and to do so, the metadata field group stl_subtitle must be used. The group should be placed within a timespan corresponding to the in- and out timecodes for when the subtitles should be displayed.

Example;

<MetadataDocument xmlns="http://xml.vidispine.com/schema/vidispine">
  <timespan start="10@PAL" end="100@25">
    <group>
      <name>stl_subtitle</name>
      <field><name>stl_justification</name><value>left</value></field>
      <field><name>stl_vertical</name><value>6</value></field>
      <field><name>stl_text</name><value>some text&#13;&#10;actually two lines</value></field>
    </group>
  </timespan>
</MetadataDocument>
CODE

More information about all different fields that can be used within the "stl-subtitle" group;

http://apidoc.vidispine.com/latest/item/metadata/subtitles.html#subtitle-metadata-fields-and-groups