[vlc] how to dump subtitles produced by dvbsub.c to an image file

[Selçuk Cihan]

Hi, i need to save dvb subtitles as images (say png). I added a method
(call it png_save) to dvbsub.c and invoked it inside the method:
static subpicture_t *render( decoder_t *p_dec )

I could not figure out how vlc stores the subtitle image (is it YUV?
is it an index into a table?). It is not plain RGBA. What i need is to
get rgba value for each pixel of the subtitle image. Currently, i read
values from p_src = p_region->p_pixbuf for each region. But i do not
know how to interpret them and convert to rgba. Any help truely
appreciated.