This is the input.
relaxed@samson:~/encodes/dump/test$ ffmpeg -i ../stream.dump 
FFmpeg version SVN-r11668, Copyright (c) 2000-2008 Fabrice Bellard, et al.
  configuration: --extra-cflags=-I/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/include --extra-ldflags=-L/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/lib --prefix=/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am --disable-ffserver --enable-libmp3lame --enable-libfaac --enable-libfaad --enable-pthreads --enable-gpl --enable-liba52 --disable-vhook --enable-libx264 --enable-swscaler --enable-pp --enable-libdc1394 --enable-libtheora --enable-libvorbis
  libavutil version: 49.6.0
  libavcodec version: 51.50.0
  libavformat version: 52.7.0
  libavdevice version: 52.0.0
  built on Jan 30 2008 10:29:56, gcc: 4.2.3 20080114 (prerelease) (Debian 4.2.2-7)
Input #0, mpeg, from '../stream.dump':
  Duration: 00:47:34.9, start: 0.192267, bitrate: 6144 kb/s
    Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x480 [PAR 8:9 DAR 4:3], 9800 kb/s, 29.97 tb(r)
    Stream #0.1[0x20]: Subtitle: dvdsub
    Stream #0.2[0x21]: Subtitle: dvdsub
    Stream #0.3[0x22]: Subtitle: dvdsub
    Stream #0.4[0x80]: Audio: liba52, 48000 Hz, 5:1, 448 kb/s
    Stream #0.5[0x81]: Audio: liba52, 48000 Hz, stereo, 192 kb/s
Must supply at least one output file



relaxed@samson:~/encodes/dump/test$ ffmpeg -t 00:00:30 -i ../stream.dump -sn -an -vcodec mpeg4 output.mkv
FFmpeg version SVN-r11668, Copyright (c) 2000-2008 Fabrice Bellard, et al.
  configuration: --extra-cflags=-I/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/include --extra-ldflags=-L/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/lib --prefix=/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am --disable-ffserver --enable-libmp3lame --enable-libfaac --enable-libfaad --enable-pthreads --enable-gpl --enable-liba52 --disable-vhook --enable-libx264 --enable-swscaler --enable-pp --enable-libdc1394 --enable-libtheora --enable-libvorbis
  libavutil version: 49.6.0
  libavcodec version: 51.50.0
  libavformat version: 52.7.0
  libavdevice version: 52.0.0
  built on Jan 30 2008 10:29:56, gcc: 4.2.3 20080114 (prerelease) (Debian 4.2.2-7)
Input #0, mpeg, from '../stream.dump':
  Duration: 00:47:34.9, start: 0.192267, bitrate: 6144 kb/s
    Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x480 [PAR 8:9 DAR 4:3], 9800 kb/s, 29.97 tb(r)
    Stream #0.1[0x20]: Subtitle: dvdsub
    Stream #0.2[0x21]: Subtitle: dvdsub
    Stream #0.3[0x22]: Subtitle: dvdsub
    Stream #0.4[0x80]: Audio: liba52, 48000 Hz, 5:1, 448 kb/s
    Stream #0.5[0x81]: Audio: liba52, 48000 Hz, stereo, 192 kb/s
Output #0, matroska, to 'output.mkv':
    Stream #0.0: Video: mpeg4, yuv420p, 720x480 [PAR 8:9 DAR 4:3], q=2-31, 200 kb/s, 29.97 tb(c)
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding
frame=  901 fps=148 q=31.0 Lsize=    1697kB time=30.1 bitrate= 462.4kbits/s    
video:1689kB audio:0kB global headers:0kB muxing overhead 0.475278%



This is the output.
relaxed@samson:~/encodes/dump/test$ ffmpeg -i output.mkv 
FFmpeg version SVN-r11668, Copyright (c) 2000-2008 Fabrice Bellard, et al.
  configuration: --extra-cflags=-I/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/include --extra-ldflags=-L/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am/lib --prefix=/home/relaxed/.build.pkgs/custom/ffmpeg-01.30.08_10.23am --disable-ffserver --enable-libmp3lame --enable-libfaac --enable-libfaad --enable-pthreads --enable-gpl --enable-liba52 --disable-vhook --enable-libx264 --enable-swscaler --enable-pp --enable-libdc1394 --enable-libtheora --enable-libvorbis
  libavutil version: 49.6.0
  libavcodec version: 51.50.0
  libavformat version: 52.7.0
  libavdevice version: 52.0.0
  built on Jan 30 2008 10:29:56, gcc: 4.2.3 20080114 (prerelease) (Debian 4.2.2-7)
[matroska @ 0x84c52f4]Ignoring seekhead entry for ID=0x1549a966
[matroska @ 0x84c52f4]Ignoring seekhead entry for ID=0x1654ae6b
[matroska @ 0x84c52f4]Ignoring seekhead entry for ID=0x114d9b74
[matroska @ 0x84c52f4]Unknown entry 0x73a4 in info header

Seems stream 0 codec frame rate differs from container frame rate: 30000.00 (30000/1) -> 29.92 (359/12)
Input #0, matroska, from 'output.mkv':
  Duration: 00:00:30.0, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: mpeg4, yuv420p, 720x480 [PAR 8:9 DAR 4:3], 29.92 tb(r)
Must supply at least one output file

Here mplayer sees the output as 25 fps
relaxed@samson:~/encodes/dump/test$ mplayer -identify -frames 0 -ao null -vo null  -vc dummy output.mkv 2>/dev/null | grep ID_
ID_VIDEO_ID=0
ID_FILENAME=output.mkv
ID_DEMUXER=mkv
ID_VIDEO_FORMAT=mp4v
ID_VIDEO_BITRATE=0
ID_VIDEO_WIDTH=720
ID_VIDEO_HEIGHT=480
ID_VIDEO_FPS=25.000
ID_VIDEO_ASPECT=1.3333
ID_LENGTH=30.06