Add Caption support to paella
Extracted from https://github.com/opencast/opencast/pull/15
To add the captions the player needs:
1) to find the caption element
The player can search for a flavor, ¿in catalogs and attachments?
2) its language
The player can search for a "lang:XX" tag.
When using the IBM Watson service, the results are converted to a playable format via the CaptionService. The CaptionService already tags the element with "lang:en"
For other caption sources e.g. manually uploaded captions, the workflow would be responsible for setting the "lang:XX" tag
3) its format.
The captions format (dfxp/vtt) could be figured out by the mime-type