If you are looking at Tk you also might be interested in TkZinc. I have not used it, but it might be fun to play around with ways to display animated karaoke lyrics. It does allow opengl but I have not found info about video.

"If you need alpha-transparency, color gradient, rotating or zooming images and graphics, structuring your graphic Canvas application in hierarchical groups, using affine transformations, displaying multicontour surfaces, complex clipping, or designing a performant radar display, then TkZinc is the widget you need, while being very similar to the Canvas."

wxperl might also work for you. Incidentally it isn't perl but I believe mplayer can be used to show subtitles from a text subtitle file in nice antialiased fonts, like OSD apparently, though I am not sure if this can be driven live i.e. from stdout of a perl script.

Hope this helps, tell us how it goes!