gajdot@gajdot:~/ffmpeg_test$ ./ffmpeg -i first.MOV -i second.MOV -filter_complex "[0:a][1:a]amerge, pan=stereo|c0=0.9*c0+0.1*c2|c1=0.9*c1+0.1*c3[a]" -map [a] output.mp3
ffmpeg version N-59158-g745c40a Copyright (c) 2000-2013 the FFmpeg developers
  built on Dec 17 2013 05:32:25 with gcc 4.6 (Debian 4.6.3-1)
  configuration: --prefix=/root/ffmpeg-static/64bit --extra-cflags='-I/root/ffmpeg-static/64bit/include -static' --extra-ldflags='-L/root/ffmpeg-static/64bit/lib -static' --extra-libs='-lxml2 -lexpat -lfreetype' --enable-static --disable-shared --disable-ffserver --disable-doc --enable-bzlib --enable-zlib --enable-postproc --enable-runtime-cpudetect --enable-libx264 --enable-gpl --enable-libtheora --enable-libvorbis --enable-libmp3lame --enable-gray --enable-libass --enable-libfreetype --enable-libopenjpeg --enable-libspeex --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-version3 --enable-libvpx
  libavutil      53.  0.100 / 53.  0.100
  libavcodec     55. 45.101 / 55. 45.101
  libavformat    55. 22.100 / 55. 22.100
  libavdevice    55.  5.102 / 55.  5.102
  libavfilter     4.  0.100 /  4.  0.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'first.MOV':
  Metadata:
    major_brand     : qt
    minor_version   : 537331968
    compatible_brands: qt  CAEP
    creation_time   : 2013-09-07 00:39:52
  Duration: 00:00:07.97, start: 0.000000, bitrate: 44582 kb/s
    Stream #0:0(eng): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuvj420p(pc, smpte170m), 1920x1080, 43037 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 48k tbc (default)
    Metadata:
      creation_time   : 2013-09-07 00:39:52
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2013-09-07 00:39:52
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'second.MOV':
  Metadata:
    major_brand     : qt
    minor_version   : 537331968
    compatible_brands: qt  CAEP
    creation_time   : 2013-10-27 19:43:21
  Duration: 00:00:30.52, start: 0.000000, bitrate: 40865 kb/s
    Stream #1:0(eng): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuvj420p(pc, smpte170m), 1920x1080, 39325 kb/s, 25 fps, 25 tbr, 25k tbn, 50k tbc (default)
    Metadata:
      creation_time   : 2013-10-27 19:43:21
    Stream #1:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2013-10-27 19:43:21
File 'output.mp3' already exists. Overwrite ? [y/N] y
[Parsed_amerge_0 @ 0x269ff20] No channel layout for input 1
[Parsed_amerge_0 @ 0x269ff20] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
Output #0, mp3, to 'output.mp3':
  Metadata:
    major_brand     : qt
    minor_version   : 537331968
    compatible_brands: qt  CAEP
    TSSE            : Lavf55.22.100
    Stream #0:0: Audio: mp3 (libmp3lame), 48000 Hz, stereo, s16p (default)
Stream mapping:
  Stream #0:1 (pcm_s16le) -> amerge:in0
  Stream #1:1 (pcm_s16le) -> amerge:in1
  pan -> Stream #0:0 (libmp3lame)
Press [q] to stop, [?] for help
size=     125kB time=00:00:07.96 bitrate= 128.7kbits/s
video:0kB audio:125kB subtitle:0 global headers:0kB muxing overhead 0.264327%