With some codecs even 720p is too demanding on my 1.5 GHz mini. The h264 files my el cheapo camcorder recordes are too heavy:

Ram Disk:> linda:MPlayer/MPlayer Jenny:Freiburg-Kurs/videos/präp1.MOV -benchmark -lavdopts skiploopfilter=all
MPlayer SVN-r31036-4.2.4 (C) 2000-2010 MPlayer Team
150 audio & 337 video codecs

Playing Jenny:Freiburg-Kurs/videos/präp1.MOV.
libavformat file format detected.
[lavf] Video stream found, -vid 0
[lavf] Audio stream found, -aid 1
VIDEO: [H264] 1280x720 24bpp 29.970 fps 5348.1 kbps (652.8 kbyte/s)
Clip info:
major_brand: qt
minor_version: 0
compatible_brands: qt
VO: [cgx_overlay_gui] Hello!
VO: [cgx_overlay] Hello!
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264)
==========================================================================
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 2 ch, s16be, 128.0 kbit/8.33% (ratio: 16000->192000)
Selected audio codec: [ffaac] afm: ffmpeg (FFmpeg AAC (MPEG-2/MPEG-4 Audio))
==========================================================================
AHI: Using 10584 bytes per chunk and 330 Kb for buffer
AO: [ahi] 48000Hz 2ch s16be (2 bytes per sample)
Starting playback...
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
VO: [cgx_overlay] 1280x720 => 1280x720 Planar YV12
VO: [cgx_overlay] Window mode.
VO: [cgx_overlay] : window size: 1280x720.
VO: Disabling blanker
VO: [cgx_overlay] : cgxvideo.library >= 43.6 detected, using doublebuffer
VO: [cgx_overlay] : using draw_slice_420p (PLANAR) primitive


BENCHMARKs: VC: 131.194s VO: 35.682s A: 4.416s Sys: 0.401s = 171.693s
BENCHMARK%: VC: 76.4117% VO: 20.7823% A: 2.5721% Sys: 0.2338% = 100.0000%
VO: Enabling blanker

The -framedrop option makes it useable and sync'ed, but then there are really nasty framedrops (of up to more than 0.5s) during playback.