nice. adding support for more subtitle renderer would make this a perfect default renderer.
if you add support for 16/32 bit texture format you should think about adding dithering. i know the build from JanWillem32 had it maybe it can be ported:
https://forum.doom9.org/showthread.php?t=161047
16 bit should be enough so it could be tested with dx9.
there is a small thing in the OSD which is most likely irrelevant.
if an PNG is loaded with lavfilter the OSD reports inf as the frame rate but lavfilter is supposed to create a 25 HZ file:
https://abload.de/img/mpcvrosdyuk4z.png