it fixes the issue Could you check: That you SDL has accepted your format (glGetIntegerv(GL_ALPHA_BITS, bits))? That your color clear is not 1 (glClearColor). What if you clear to 0.5 and retrieve the buffer before rendering. Do you retrieve 0.5? That you alpha buffer is not write locked (glColorMask(GL_TRUE,GL_TRUE,GL_TRUE,GL_TRUE))? That you correctly clear your alpha buffer at the end of each frame? That your blend function will write the correct alpha value to the buffer?
YouTube API v3 only returning a subset of Channels