Support for new transcription management (subtitles) in Opencast 15

[ferishili]

This PR fixes #368

Description

In Opencast 15 the subtitles format has been changed drastically, in a form that the flavor now contains captions/delivery and other info like language etc. will be provided in the tags.

Solution

• In order for us to provide backward compatibility we remain by using mediapackages for upload/delete.
• The three cases (attachment, media (old) and media (new)) are covered.
• The manual transcription upload is still following captions/vtt+{lang}, simply because to maintain the difference as well as the lack of capability to upload extra tags info via add_track.

Goal

the ultimate goal is to be able to manage (delete/download/upload) manual and auto generated subtitles for an event. In order to achieve this goal it might happen that workflows has to be updated (specially republich-metadata-and-captions workflow) to cover all cases.

NOTE

Consider this PR as a beta version, because this subtitle upgrade is still fresh and might result in unexpected behaviors, therefore, this PR may have further updates

[KatrinIhler]

The manual transcription upload is still following captions/vtt+{lang}, simply because to maintain the difference as well as the lack of capability to upload extra tags info via add_track.

Is this a good idea? We should try and follow the new format.

In regards to the tagging problem see opencast/opencast#5866

[ferishili]

The manual transcription upload is still following captions/vtt+{lang}, simply because to maintain the difference as well as the lack of capability to upload extra tags info via add_track.

Is this a good idea? We should try and follow the new format.

In regards to the tagging problem see opencast/opencast#5866

At the time of implementing this, and still (the tagging feature request issue comes from Till & I to tackle this), there was no other option when using addTrack endpoint to include tags. Also, this feature goes back to almost 3 years ago and there are many institutions that are still using attachment! So removing this feature was not an option, but to maintain the old flavor!

As soon as the tagging is possible via the endpoint, we need to update it here as well!

[KatrinIhler]

@ferishili Okay, I can see why backwards compatibility would be important. And if this will support the new use case as well (when the tagging PR is through), then that's fine.