We've been working on subtitle support for Miro in the subtitle branch. Yesterday, Ben merged the changes into the master branch. As of this morning, nightly builds have subtitle support. Yay!
There are still a few things to implement and the code hasn't had much of a chance to settle. Also, there are still some things I think should get refactored and it's likely we'll be tweaking the interface going forward as we use it more.
Still, it's good to have landed the bulk of this feature. It's probably not wildly useful yet, but it gives us some ground work towards building better subtitle distribution/creation infrastructure going forward.