ffmpeg -i input.mkv -map_metadata -1 -map 0:0 -map 0:1 -map 0:1 -c:v copy -c:a:1 copy -c:a:0 libfdk_aac -b:a:0 128k -ac 2 -filter:a:0 "volume=10dB" -metadata:s:a:1 language="English (Surround)" -metadata:s:a:0 language="English (Stereo)" output.mkv


ffmpeg version 2.5.3 Copyright (c) 2000-2015 the FFmpeg developers
  built on Jan 11 2015 17:53:45 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --extra-libs=-ldl --prefix=/opt/ffmpeg --enable-avresample --disable-debug --enable-nonfree --enable-gpl --enable-version3 --enable-libpulse --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-decoder=amrnb --disable-decoder=amrwb --enable-libx264 --enable-libx265 --enable-libfdk-aac --enable-libvorbis --enable-libmp3lame --enable-libopus --enable-libvpx --enable-libspeex --enable-libass --enable-avisynth --enable-libsoxr --enable-libxvid --enable-libvo-aacenc --enable-libvidstab
  libavutil      54. 15.100 / 54. 15.100
  libavcodec     56. 13.100 / 56. 13.100
  libavformat    56. 15.102 / 56. 15.102
  libavdevice    56.  3.100 / 56.  3.100
  libavfilter     5.  2.103 /  5.  2.103
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, matroska,webm, from 'input.mkv':
  Metadata:
    ENCODER         : Lavf56.15.102
  Duration: 01:49:18.12, start: 0.083000, bitrate: 5718 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 1280x544, SAR 1:1 DAR 40:17, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Stream #0:1: Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s
Output #0, matroska, to 'output.mkv':
  Metadata:
    encoder         : Lavf56.15.102
    Stream #0:0: Video: h264 (H264 / 0x34363248), yuv420p, 1280x544 [SAR 1:1 DAR 40:17], q=2-31, 23.98 fps, 1k tbn, 1k tbc (default)
    Stream #0:1(English (Stereo)): Audio: aac (libfdk_aac) ([255][0][0][0] / 0x00FF), 48000 Hz, stereo, s16, 128 kb/s
    Metadata:
      encoder         : Lavc56.13.100 libfdk_aac
    Stream #0:2(English (Surround)): Audio: dts ([1] [0][0] / 0x2001), 48000 Hz, 5.1(side), 1536 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (dts (dca) -> aac (libfdk_aac))
  Stream #0:1 -> #0:2 (copy)
Press [q] to stop, [?] for help
frame=157235 fps=507 q=-1.0 Lsize= 4682742kB time=01:49:18.04 bitrate=5849.5kbits/s
video:3364729kB audio:1310485kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.160995%