ffmpeg -i audio.mp2 -i video.mp4 -map -0 -map -1 -map 1:v:0 -map 0:a:0 -acodec copy -vcodec copy output.mp4

ffmpeg version N-65616-g7cdef77 Copyright (c) 2000-2014 the FFmpeg developers
  built on Aug 13 2014 23:17:18 with gcc 4.8.3 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-lib
modplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrw
b --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinge
r --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --en
able-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis
 --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-
libx265 --enable-libxavs --enable-libxvid --enable-decklink --enable-zlib
  libavutil      54.  3.100 / 54.  3.100
  libavcodec     56.  0.100 / 56.  0.100
  libavformat    56.  1.100 / 56.  1.100
  libavdevice    56.  0.100 / 56.  0.100
  libavfilter     5.  0.100 /  5.  0.100
  libswscale      3.  0.100 /  3.  0.100
  libswresample   1.  0.100 /  1.  0.100
  libpostproc    53.  0.100 / 53.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'C:\BeSweet\out.m4a':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: M4A mp42isom
    creation_time   : 2014-08-31 23:27:16
    iTunSMPB        :  00000000 00000A40 00000040 0000000000270180 00000000 0000
0000 00000000 00000000 00000000 00000000 00000000 00000000
    encoder         : Nero AAC codec / 1.5.4.0
  Duration: 00:00:53.31, start: 0.000000, bitrate: 136 kb/s
    Chapter #0.0: start 0.054667, end 53.312000
    Metadata:
      title           :
    Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 13
4 kb/s (default)
    Metadata:
      creation_time   : 2014-08-31 23:27:16
      handler_name    : Sound Media Handler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'video.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.1.100
  Duration: 00:00:53.28, start: 0.000000, bitrate: 1054 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 704x394 [
SAR 197:198 DAR 16:9], 1049 kb/s, 50 fps, 50 tbr, 90k tbn, 100 tbc (default)
    Metadata:
      handler_name    : VideoHandler
Stream map '0' matches no streams.