For some time now, GStreamer has supported subtitles. One of the players using this feature is Totem. Subtitles are automatically supported if you use the playbin element. Currently, Ogm and Matroska plain-text subtitles and external subtitle files in microDVD, MPsub and Subrip format are supported. It would be nice to support more types of subtitles, particularly the ones in external text files, since those are very easy to add.

It's a good idea to support as many media formats as possible. In addition, our subtitle support is not very wide yet, and we hope to change that.

External subtitle files are handled by the subparse element (in gst-plugins/gst/subparse/gstsubparse.c). Each subtitle has three functions available - one for initialization, one for reading a single subtitle and one to deinitialize. For each new subtitle format, adding those three functions is enough. After that, test the newly added code in Totem. If all is well, it should just work.
It is also possible to add more subtitle support to particular demuxers, e.g. Ogg/Ogm or Matroska. In that case look at the code of that particular demuxer and it there.

Ronald, Thomas

EASY: three functions per format, and no code involved elsewhere.