ffmpeg -i video.mp4 -sameq video.rmvb
ffmpeg version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Jun 12 2012 16:52:09 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a future release. Please use avconv instead.
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2012-03-13 21:11:41
  Duration: 00:05:05.36, start: 0.000000, bitrate: 327 kb/s
    Stream #0.0(und): Video: h264 (Constrained Baseline), yuv420p, 480x360, 233 kb/s, 25 fps, 25 tbr, 50 tbn, 50 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 91 kb/s
    Metadata:
      creation_time   : 2012-03-13 21:11:41
Unable to find a suitable output format for 'video.rmvb'