Yes, the mplayer messages in your terminal program say exactly that, not enough cpu power. Guess what? If you use mplayer plug the mplayer-plugin; or xine plus the xine-plugin; or totem plus the totem-plugin; the latest google-chrome, the one that slitaz fetches for you, turns into a high-power video player with 720p (maybe more), and a built-in acceleration modules (ffmpegsumo.so in /opt/google/chrome) that easily beats any built-in accelerator chip. If you are running a "non-accelerated" ati driver on slitaz, chances are this google-chrome would beat any "accelerated ati driver" hands down.
The way to play a file with it is to point the browser by naming the directory of the file. E. g.,
/home/tux/Videos/BigBuckBunny.ogg
/home/tux/Videos/Sexy.mpeg4
When you do this, you get the kind of video playback you can use to run your television monitor with.
Of course, on a Cedarview system, this trick only works with non-slitaz distributions that don't insist on running the slitaz vesa driver. Even on the slitaz vesa driver, though, you get the bouncing glass ball, rarely seen on any Linux box, and an occasional score in the 800s, using the peacekeeper benchmark. The browser does its best to motion compensate the slitaz vesa driver, but the results are mediocre to say the least.
Too bad slitaz hasn't been made safe for the 'adaptation-pc' kernel and modules, available free from tizen.com or from the MeeGo archives.