Someone

ffmpeg -f ac3 -i VM_audio.mpa -f mp4 -acodec aac -ab 192k VM_audio.mp4
FFmpeg version SVN-rUNKNOWN, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --prefix=/usr --libdir=/usr/lib --shlibdir=/usr/lib --mandir=/usr/share/man --e
nable-static --enable-shared --cc=i686-pc-linux-gnu-gcc --disable-altivec --disable-debug --disa
ble-audio-oss --disable-dv1394 --disable-network --disable-opts --enable-libmp3lame --enable-lib
vorbis --enable-libogg --enable-libtheora --enable-libogg --enable-liba52 --enable-pthreads --en
able-xvid --enable-x11grab --enable-libogg --enable-libdts --enable-x264 --enable-libfaad --enab
le-libfaac --enable-gpl --enable-pp --disable-strip
  libavutil version: 49.4.0
  libavcodec version: 51.40.2
  libavformat version: 51.11.0
  built on Apr 27 2007 06:59:26, gcc: 4.1.1 (Gentoo 4.1.1-r3)
Input #0, ac3, from 'VM_audio.mpa':
  Duration: 00:41:17.2, start: 0.000000, bitrate: 384 kb/s
  Stream #0.0: Audio: ac3, 48000 Hz, 5:1, 384 kb/s
Output #0, mp4, to 'VM_audio.mp4':
  Stream #0.0: Audio: aac, 48000 Hz, 5:1, 192 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
No accelerated IMDCT transform found


ID_AUDIO_ID=0
ID_FILENAME=VM_audio.mp4
ID_DEMUXER=mov
ID_AUDIO_FORMAT=mp4a
ID_AUDIO_BITRATE=0
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=2
ID_LENGTH=1222.63
ID_AUDIO_BITRATE=128000
ID_AUDIO_RATE=48000
ID_AUDIO_NCH=2
ID_AUDIO_CODEC=faad