I'm sorry, sir, I'm afraid you cannot expect the impossible from mplayer - to use a codec where there isn't one.
On my ubuntu:
If you don't have it you can fall back on the xvid codec, but it tends to not be as nice.
On my ubuntu:
$ mencoder -ovc help
MEncoder 2:0.99+1.0pre7try2+cvs20060117-0ubuntu8 (C) 2000-2006 MPlayer Team
CPU: Intel Pentium 4/Celeron 4 Northwood; Pentium 4 EE/Xeon Prestonia,Gallatin (Family: 15, Stepping: 4)
CPUflags: Type: 15 MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.
91 audio & 204 video codecs
Available codecs:
copy - frame copy, without re-encoding. Doesn't work with filters.
frameno - special audio-only file for 3-pass encoding, see DOCS.
raw - uncompressed video. Use fourcc option to set format explicitly.
nuv - nuppel video
lavc - libavcodec codecs - best quality!
vfw - VfW DLLs, currently only AVID is supported.
qtvideo - QuickTime DLLs, currently only SVQ1/3 are supported.
libdv - DV encoding with libdv v0.9.5
xvid - XviD encoding
x264 - H.264 encoding
MEncoder 2:0.99+1.0pre7try2+cvs20060117-0ubuntu8 (C) 2000-2006 MPlayer Team
CPU: Intel Pentium 4/Celeron 4 Northwood; Pentium 4 EE/Xeon Prestonia,Gallatin (Family: 15, Stepping: 4)
CPUflags: Type: 15 MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.
91 audio & 204 video codecs
Available codecs:
copy - frame copy, without re-encoding. Doesn't work with filters.
frameno - special audio-only file for 3-pass encoding, see DOCS.
raw - uncompressed video. Use fourcc option to set format explicitly.
nuv - nuppel video
lavc - libavcodec codecs - best quality!
vfw - VfW DLLs, currently only AVID is supported.
qtvideo - QuickTime DLLs, currently only SVQ1/3 are supported.
libdv - DV encoding with libdv v0.9.5
xvid - XviD encoding
x264 - H.264 encoding
