Convert rmvb to mp4

convert rmvb to mp4 on Ubuntu 8.04:

$mencoder -o temp.avi -ovc lavc -oac mp3lame rmvb_sample.rmvb
MEncoder 2:1.0~rc2-0ubuntu13.1 (C) 2000-2007 MPlayer Team
CPU: Intel(R) Celeron(R) CPU 3.06GHz (Family: 15, Model: 4, Stepping: 9)
CPUflags: Type: 15 MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.
success: format: 0 data: 0x0 - 0x3096000
REAL file format detected.
Stream description: Audio Stream
Stream mimetype: audio/x-pn-realaudio
[real] Audio stream found, -aid 0
Stream description: Video Stream
Stream mimetype: video/x-pn-realvideo
[real] Video stream found, -vid 1
Stream mimetype: logical-fileinfo
Something went wrong, no index chunk found on given address (289412565)
VIDEO: [RV40] 352x288 24bpp 30.000 fps 0.0 kbps ( 0.0 kbyte/s)
[V] filefmt:11 fourcc:0x30345652 size:352x288 fps:30.00 ftime:=0.0333
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 44100 Hz, 2 ch, s16le, 96.5 kbit/6.84% (ratio: 12058->176400)
Selected audio codec: [ffcook] afm: ffmpeg (FFmpeg COOK audio decoder)
==========================================================================
Opening video filter: [expand osd=1]
Expand: -1 x -1, -1 ; -1, osd: 1, aspect: 0.000000, round: 1
==========================================================================
Opening video decoder: [realvid] RealVideo decoder
Selected video codec: [rv3040] vfm: realvid (Linux RealPlayer 10 RV30/40 decoder)
==========================================================================
MP3 audio selected.
VDec: vo config request - 352 x 288 (preferred colorspace: Planar I420)
VDec: using Planar I420 as output csp (no 0)
Movie-Aspect is 1.22:1 - prescaling to correct movie aspect.
videocodec: libavcodec (352x288 fourcc=34504d46 [FMP4])
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.
Pos: 0.0s 1f ( 0%) 0.00fps Trem: 2min 10mb A-V:0.000 [0:0]
Skipping frame!
Pos: 0.0s 2f ( 0%) 0.00fps Trem: 2min 11mb A-V:0.003 [0:0]
...