ffmpeg -f ac3 -i VM_audio.mpa -f mp4 -acodec aac -ab 192k VM_audio.mp4
FFmpeg version SVN-r8872, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --prefix=/var/geoff/ffmpeg --enable-static --enable-shared --disable-altivec --disable-debug --disable-audio-oss --disable-dv1394 --disable-network --disable-opts --enable-libmp3lame --enable-libvorbis --enable-libogg --enable-libtheora --enable-liba52 --enable-pthreads --enable-xvid --enable-x11grab --enable-libdts --enable-x264 --enable-libfaad --enable-libfaac --enable-gpl --enable-pp --disable-strip
  libavutil version: 49.4.0
  libavcodec version: 51.40.4
  libavformat version: 51.12.1
  built on May  2 2007 12:27:18, 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

midentify:
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

mplayer:
FAAD: compressed input bitrate missing, assuming 128kbit/s!
AUDIO: 48000 Hz, 2 ch, s16le, 128.0 kbit/8.33% (ratio: 16000->192000)