files)The timing of the raster is determined by t= tags contained within
  the tags. For a  demonstration of karaoke refer to the sample file attached.

* Support for bi-directional text needs to behave inside karaoke
  tags. (In right to left text the raster needs to move from right to left
  instead of left to right - it is supporting this feature that makes this
  patch a little more complicated than it would otherwise be)

* Made the internal handling of font color and alpha tags more consistent
  and convenient in a few places by storing in one variable as AARRGGBB,
  rather than 2.

* Some cleanup of other code.

Patch by Bernie Purcell.