From W3C Wiki
At the time of this writing:
- A first set of users of IMSC are interested in referencing IMSC in the near-term and in its current form, which is essentially based on W3C Member Submission (07 June 2013) and TTML 1. A second set of users of IMSC have expressed interest in a more extended form that would be dependent on TTML2.
- Uncertainty remains with TTML 2 development and implementation availability. Implementations of W3C Member Submission (07 June 2013) exist.
Per the March 27 telecon, the plan is to deliver of IMSC as two versions:
- IMSC 1.0, published first, will be based on TTML 1 and follow closely W3C Member Submission (07 June 2013).
- IMSC 2.0, published second, will be based on TTML 2 and a superset of IMSC 1.0. Development will roughly match TTML2 in milestones.
Please see TTWG Publications for the latest status of both specifications