add TTML_TO_PARSE event
Created by: nicosang
Hi,
this PR has to add the new event called TTML_TO_PARSE. This event is triggered before ttml content is parsing by imsc1 library. In MSS use case, it allows to replace wrong namespaces according to IMSC1 point of view. A test can be made with mss stream Prince Of Persia - Live. Subtitles style is not taken into a count but text is correctly shown.
Nico