The size of the VBV doesn't matter ( it's around a second while a complicate scene often lasts more than that )The max bitrate does matters, since it's completely correlated to the decoding time. Average bitrate doesn't ( ought not ) matter when it comes to material limitations, since it's not correlated. Finally, average bitrate isn't written in the video stream. What is written is the maximum bitrate, when there is one. Of course, all that is true for h264 in general. PSP seems to love useless limitations, so a limitation on the average bitrate, though it makes to sense at all, wouldn't surprise me either...