When I try to play MP4 files in mplayer, after a few seconds I get the "Your system is too SLOW to play this!" warning and the video starts lagging behind the audio. It only happens with MP4s, and seems to happen with just about all of them. mplayer doesn't seem to be overtaxing my system, it's just something with playing that particular format. I tried all the mplayer suggestions (different video driver, -framedrop, etc.); the only one that even partially helps is -autosync 30, but that's a hack. What could be wrong? How do I go about debugging/fixing it?
Edit: My video card is an nVidia; I use the official drivers. My available video output drivers according to mplayer are:
xv X11/Xv
gl_nosw OpenGL no software rendering
x11 X11 ( XImage/Shm )
xover General X11 driver for overlay capable video output drivers
gl OpenGL
gl2 X11 (OpenGL) - multiple textures version
matrixview MatrixView (OpenGL)
null Null video output
mpegpes MPEG-PES file
yuv4mpeg yuv4mpeg output for mjpegtools
png PNG file
jpeg JPEG file
I haven't tried any other players (I don't think I even have any), but I'll try installing another one and see if it has the same problem. I forgot to mention that I have this problem on multiple computers, but they all have essentially the same setup so it's probably a common cause
-vo) in mplayer, what video driver(s) in X?