kate: port Kate subtitle plugin to 1.0

Submitted by Brendan Long

Link to original bug (#697071)

Description

Created attachment 240329
Patch to port Kate subtitles to 1.0

I need Kate plugins to work for a project I'm working on, but it hasn't been ported yet, so I went through and did some work on it myself. The plugin seems to work with this patch, but the overlay subtitles aren't showing up, so I assume I missed something.

If I run it through a test program which attaches buffer probes to every pad, I see all of the subtitles, but they don't show up on the video.

Could someone take a look at this? I can work on it more, but I'm not sure what I'm missing.

Patch 240329, "Patch to port Kate subtitles to 1.0":
0001-Port-Kate-subtitles-to-GStreamer-1.0.patch