Prevent psmfplayer from loading too many mpeg frames at once

Fixes #4550 again.  Before these changes, it fills the video buffer and discards audio data that doesn't fit.  This worked before when audio data was immediately demuxed, but now that happens on first read.

Also, seems like psmfplayer doesn't bother selecting the proper video/audio streams, but I'm not sure...

Anyway, Naruto still works this way too.

Without the cap on adding too much data at once, there is a slight but noticeable pause after the first frame/audio samples, before the video continues playing.  I left the cap generously high in case it affects compatibility, but this kills the pause for me.

-[Unknown]