kmplayer (and others based on mplayer) do not use hw acceleration and thus should fail on some vids that media player should succeed in playing if you have 720p vid libraries enabled. Media player is an integrated component and that means it marshals more resources when working and that takes time.

Nonetheless, on my setup (720p enabled, CSSU-T, kernel power and dsp overclock) and after a reboot, media player plays (image visible) a 720x432 h.264 video after between 4 to 8 secs has elapsed. Not too shabby. Smaller vids start immediately.

And yes, the dsp voltage can go wacky and trying to play HD stuff there you will sit into eternity... until a reboot sorts things out.