OGG on STBlib is just for music or run videos?
I'm using FREEGLut, GLUT and OpenGL with STB libs to learn a little bit, and i wanna to run a ogg video in a part of the screen?
It support video transparency too?

stb has vorbis decoder than decodes vorbis format from ogg container.
For video you'll need different library. If it is theora video then libtheora would work.