ffmpeg -i Elfen\ Lied\ 1.avi -vcodec mpeg4 -b 717000 -s 320x240 -r 29.97 -f mp4 -acodec aac -ar 24000 -ab 32000 test.mp4 
FFmpeg version SVN-rUNKNOWN, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man --enable-static --enable-shared --cc=x86_64-pc-linux-gnu-gcc --disable-altivec --disable-debug --disable-audio-oss --disable-v4l --disable-v4l2 --disable-dv1394 --disable-opts --enable-libmp3lame --enable-libvorbis --enable-libogg --enable-libtheora --enable-libogg --enable-liba52 --enable-pthreads --enable-libxvid --enable-x11grab --enable-libogg --enable-libx264 --enable-libfaad --enable-libfaac --enable-libamr-nb --enable-libamr-wb --enable-gpl --enable-pp --disable-strip
  libavutil version: 49.4.0
  libavcodec version: 51.40.4
  libavformat version: 51.12.1
  built on Nov 13 2007 10:05:29, gcc: 4.1.2 (Gentoo 4.1.2)

Seems stream 0 codec frame rate differs from container frame rate: 23.00 (65535/2849) -> 23.00 (230000/10000)
Input #0, avi, from 'Elfen Lied 1.avi':
  Duration: 00:24:31.3, start: 0.000000, bitrate: 1243 kb/s
  Stream #0.0: Video: mpeg4, yuv420p, 640x480, 23.00 fps(r)
  Stream #0.1: Audio: pcm_u8, 48000 Hz, mono, 384 kb/s
Unknown codec 'aac'