convert avi to webm

$ time mencoder -ovc lavc -oac lavc -of lavf -lavfopts format=webm -lavcopts acodec=vorbis:vcodec=libvpx -ffourcc VP80 test.avi -o test.webm

MEncoder SVN-r32624-4.5.1 (C) 2000-2010 MPlayer Team
success: format: 0  data: 0x0 - 0xb3d3c4
AVI file format detected.
[aviheader] Video stream found, -vid 0
[aviheader] Audio stream found, -aid 1
VIDEO:  [DIVX]  320x240  24bpp  18.000 fps  360.6 kbps (44.0 kbyte/s)
[V] filefmt:3  fourcc:0x58564944  size:320x240  fps:18.000  ftime:=0.0556
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 22050 Hz, 2 ch, s16le, 64.0 kbit/9.07% (ratio: 8000->88200)
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
** MUXER_LAVF *****************************************************************
REMEMBER: MEncoder's libavformat muxing is presently broken and can generate
INCORRECT files in the presence of B-frames. Moreover, due to bugs MPlayer
will play these INCORRECT files as if nothing were wrong!
*******************************************************************************
OK, exit.
Opening video filter: [expand osd=1]
Expand: -1 x -1, -1 ; -1, osd: 1, aspect: 0.000000, round: 1
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffodivx] vfm: ffmpeg (FFmpeg MPEG-4)
==========================================================================
Forcing output FourCC to 30385056 [VP80].
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
videocodec: libavcodec (320x240 fourcc=30385056 [VP80])
[libvpx @ 0xaa99e0]v0.9.5
VIDEO CODEC ID: 146
AUDIO CODEC ID: 15005, TAG: 0
Writing header...
[webm @ 0xa3bde0]Codec for stream 0 does not use global headers but container format requires global headers
[webm @ 0xa3bde0]Codec for stream 1 does not use global headers but container format requires global headers
Pos: 216.3s   3893f (100%) 37.51fps Trem:   0min  20mb  A-V:0.051 [783:8]

Flushing video frames.
Writing index...

Video stream:  783.501 kbit/s  (97937 B/s)  size: 21181737 bytes  216.278 secs  3893 frames

Audio stream:    8.585 kbit/s  (1073 B/s)  size: 232083 bytes  216.271 secs

real 1m44.368s
user 1m43.459s
sys 0m0.144s

$ mplayer test.webm

MPlayer SVN-r32624-4.5.1 (C) 2000-2010 MPlayer Team

Playing test.webm.
libavformat file format detected.
[matroska,webm @ 0x1ae17c0] Estimating duration from bitrate, this may be inaccurate
[lavf] stream 0: video (vp8), -vid 0
[lavf] stream 1: audio (vorbis), -aid 0
VIDEO:  [VP80]  320x240  0bpp  18.000 fps    0.0 kbps ( 0.0 kbyte/s)
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffvp8] vfm: ffmpeg (FFmpeg VP8)
==========================================================================
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 22050 Hz, 2 ch, s16le, 0.0 kbit/0.00% (ratio: 0->88200)
Selected audio codec: [ffvorbis] afm: ffmpeg (FFmpeg Vorbis)
==========================================================================
AO: [null] 22050Hz 2ch s16le (2 bytes per sample)
Starting playback...
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [xv] 320x240 => 320x240 Planar YV12 
A:   6.4 V:   6.4 A-V: -0.000 ct:  0.046   0/  0  6%  0%  0.3% 0 0 

$ ls -la test.*

-rw-r--r-- 1 user user 11785156 Aug 21  2009 test.avi
-rw-r--r-- 1 user user 21474219 Nov 21 21:50 test.webm

$ midentify test.avi

ID_VIDEO_ID=0
ID_AUDIO_ID=1
ID_CLIP_INFO_NAME0=Software
ID_CLIP_INFO_VALUE0=MEncoder\ SVN-r29214\(20090422-gcc4.3.3\)
ID_CLIP_INFO_N=1
ID_FILENAME=test.avi
ID_DEMUXER=avi
ID_VIDEO_FORMAT=DIVX
ID_VIDEO_BITRATE=360608
ID_VIDEO_WIDTH=320
ID_VIDEO_HEIGHT=240
ID_VIDEO_FPS=18.000
ID_VIDEO_ASPECT=0.0000
ID_AUDIO_FORMAT=85
ID_AUDIO_BITRATE=64000
ID_AUDIO_RATE=0
ID_AUDIO_NCH=0
ID_START_TIME=0.00
ID_LENGTH=216.28
ID_SEEKABLE=1
ID_CHAPTERS=0
ID_VIDEO_CODEC=ffodivx
ID_AUDIO_BITRATE=64000
ID_AUDIO_RATE=22050
ID_AUDIO_NCH=2
ID_AUDIO_CODEC=mp3
ID_EXIT=EOF

$ midentify test.webm

ID_VIDEO_ID=0
ID_AUDIO_ID=0
ID_FILENAME=test.webm
ID_DEMUXER=lavfpref
ID_VIDEO_FORMAT=VP80
ID_VIDEO_BITRATE=0
ID_VIDEO_WIDTH=320
ID_VIDEO_HEIGHT=240
ID_VIDEO_FPS=18.000
ID_VIDEO_ASPECT=1.3333
ID_AUDIO_FORMAT=22127
ID_AUDIO_BITRATE=0
ID_AUDIO_RATE=22050
ID_AUDIO_NCH=2
ID_START_TIME=0.00
ID_LENGTH=216.28
ID_SEEKABLE=1
ID_CHAPTERS=0
ID_VIDEO_CODEC=ffvp8
ID_AUDIO_BITRATE=0
ID_AUDIO_RATE=22050
ID_AUDIO_NCH=2
ID_AUDIO_CODEC=ffvorbis
ID_EXIT=EOF