AE Transparency Rendering Problem

Hi,
I have being trying to render my ae file with transparent BG, tried all lossless, avi, flv, with the transparency grid selected, with RGB + ALPH, Multimillion Colors, with audio, when it renders out their is a black background behind it, also tried the png sequence then imported it to the AE again, when I render it out into a .mp4 h.264 the transparency is removed and I have a black background.
Thank you.