Cannot play webm file

[kuh3h3@…]

what is this error?
Cannot find codec matching selected -vo and video format 0x30385056.

media/sdc1$ mplayer shu1.webm
MPlayer SVN-r31222-4.3.3 (C) 2000-2010 MPlayer Team
150 audio & 338 video codecs
mplayer: could not connect to socket
mplayer: No such file or directory
Failed to open LIRC support. You will not be able to use your remote control.

Playing shu1.webm.
Seek failed
libavformat file format detected.
[libvpx @ 0x8fce500]v0.9.0-22-g0270a79
[matroska @ 0x8fcaeb0]Estimating duration from bitrate, this may be inaccurate
[lavf] stream 0: video (libvpx), -vid 0
[lavf] stream 1: audio (vorbis), -aid 0
VIDEO: [VP80] 480x360 0bpp 30.000 fps 0.0 kbps ( 0.0 kbyte/s)
Opening video filter: [screenshot]
Opening video filter: [hqdn3d]
Opening video filter: [pp=de]
==========================================================================
Cannot find codec matching selected -vo and video format 0x30385056.
==========================================================================
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 44100 Hz, 2 ch, s16le, 0.0 kbit/0.00% (ratio: 0->176400)
Selected audio codec: [ffvorbis] afm: ffmpeg (FFmpeg Vorbis)
==========================================================================
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback...
A: 14.7 (14.7) of 53.9 (53.9) 2.7%

MPlayer interrupted by signal 2 in module: play_audio
A: 14.8 (14.7) of 53.9 (53.9) 2.7%
Exiting... (Quit)

[reimar]

This

150 audio & 338 video codecs

means you have an outdated codecs.conf somewhere.
You will not be able to play any new formats (and VP8 is a new format) unless you update it or just delete it.