[ffmpeg: toubles with channelsplit and amerge]
I got a video with an audio stream with 4 channels.
The goal : get 2 audios streams with stereo.
The first stream is fine (stereo preserved)
Second stream is a mixed stereo ?

[ffmpeg command]
ffmpeg -map 0:0 -map 0:1 -map 0:1 -f mov -vcodec libx264 -b:v 800k -g 5 -r 25 -acodec libfaac -ab 64000 -ar 48000 -aspect 16:9 -timecode 10:00:00:00 -metadata title=qlatest_s -metadata comment=Filiere=MultiDiff_Transcode-Destination=browse -filter_complex [0:v] crop=720:576:0:32, yadif=0:-1:0, scale=640:360;; channelsplit=channel_layout=4.0[A1][A2][A3][A4];[A1][A2] amerge=inputs=2; [A3][A4] amerge=inputs=2 -metadata:s:v:0 language=fra -metadata:s:a:0 language=fra -metadata:s:a:1 language=eng -y /mnt/isilon_import/ftp/qla/proxy/qlatest_s.mov

[ffmpeg output]
fmpeg version 2.0 Copyright (c) 2000-2013 the FFmpeg developers
  built on Sep  6 2013 14:25:53 with gcc 4.4.6 (GCC) 20110731 (Red Hat 4.4.6-3)
  configuration: --prefix=/usr/local/ffmpeg --enable-nonfree --enable-postproc --enable-swscale --enable-pthreads --enable-libx264 --enable-gpl --enable-libvorbis --enable-libfaac --enable-libmp3lame --enable-libfreetype --enable-libass
  libavutil      52. 42.100 / 52. 42.100
  libavcodec     55. 29.100 / 55. 29.100
  libavformat    55. 14.102 / 55. 14.102
  libavdevice    55.  3.100 / 55.  3.100
  libavfilter     3. 82.102 /  3. 82.102
  libswscale      2.  5.100 /  2.  5.100
  libswresample   0. 17.103 /  0. 17.103
  libpostproc    52.  3.100 / 52.  3.100
[mxf @ 0x2ee6f60] file is not seekable - not parsing footer
Guessed Channel Layout for  Input Stream #0.1 : 4.0
Input #0, mxf, from 'pipe:':
  Metadata:
    uid             : adab4424-2f25-4dc7-92ff-29bd000b0000
    generation_uid  : adab4424-2f25-4dc7-92ff-29bd000b0001
    company_name    : FFmbc
    product_name    : OP1a Muxer
    product_version : 53.6.0
    product_uid     : adab4424-2f25-4dc7-92ff-29bd000b0002
    modification_date: 2013-09-13 07:45:12
    timecode        : 10:00:00:00
  Duration: 00:04:00.76, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: mpeg2video (4:2:2), yuv422p, 720x608 [SAR 152:135 DAR 4:3], max. 50000 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc
    Stream #0:1: Audio: pcm_s16le, 48000 Hz, 4.0, s16, 3072 kb/s
No pixel format specified, yuv422p for H.264 encoding chosen.
Use -pix_fmt yuv420p for compatibility with outdated media players.
[libx264 @ 0x2f4f7a0] using SAR=1/1
[libx264 @ 0x2f4f7a0] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
[libx264 @ 0x2f4f7a0] profile High 4:2:2, level 3.0, 4:2:2 8-bit
[libx264 @ 0x2f4f7a0] 264 - core 122 - H.264/MPEG-4 AVC codec - Copyleft 2003-2012 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=18 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=5 keyint_min=1 scenecut=40 intra_refresh=0 rc_lookahead=5 rc=abr mbtree=1 bitrate=800 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mov, to '/mnt/isilon_import/ftp/qla/proxy/qlatest_s.mov':
  Metadata:
    uid             : adab4424-2f25-4dc7-92ff-29bd000b0000
    generation_uid  : adab4424-2f25-4dc7-92ff-29bd000b0001
    company_name    : FFmbc
    product_name    : OP1a Muxer
    product_version : 53.6.0
    product_uid     : adab4424-2f25-4dc7-92ff-29bd000b0002
    modification_date: 2013-09-13 07:45:12
    timecode        : 10:00:00:00
    title           : qlatest_s
    copyright       : RTBF
    comment         : Filiere=MultiDiff_Transcode-Destination=browse
    encoder         : Lavf55.14.102
    Stream #0:0(fra): Video: h264 (libx264) (avc1 / 0x31637661), yuv422p, 640x360 [SAR 1:1 DAR 16:9], q=-1--1, 800 kb/s, 12800 tbn, 25 tbc
    Stream #0:1(fra): Audio: aac (libfaac) (mp4a / 0x6134706D), 48000 Hz, stereo, s16, 64 kb/s
    Stream #0:2(eng): Audio: aac (libfaac) (mp4a / 0x6134706D), 48000 Hz, stereo, s16, 64 kb/s
Stream mapping:
  Stream #0:0 (mpeg2video) -> crop
  Stream #0:1 (pcm_s16le) -> channelsplit
  scale -> Stream #0:0 (libx264)
  amerge -> Stream #0:1 (libfaac)
  amerge -> Stream #0:2 (libfaac)
frame= 6019 fps=218 q=-1.0 Lsize=   27861kB time=00:04:00.76 bitrate= 947.9kbits/s
video:24236kB audio:3353kB subtitle:0 global headers:0kB muxing overhead 0.985647%
[libx264 @ 0x2f4f7a0] frame I:1245  Avg QP:21.32  size: 13814
[libx264 @ 0x2f4f7a0] frame P:1866  Avg QP:25.28  size:  2932
[libx264 @ 0x2f4f7a0] frame B:2908  Avg QP:25.52  size:   738
[libx264 @ 0x2f4f7a0] consecutive B-frames: 30.9% 13.4%  2.2% 53.5%
[libx264 @ 0x2f4f7a0] mb I  I16..4: 23.4% 71.9%  4.7%
[libx264 @ 0x2f4f7a0] mb P  I16..4:  8.3%  8.5%  0.1%  P16..4: 40.0%  9.6%  3.5%  0.0%  0.0%    skip:30.0%
[libx264 @ 0x2f4f7a0] mb B  I16..4:  0.1%  0.2%  0.0%  B16..8: 24.1%  1.0%  0.2%  direct: 2.5%  skip:71.8%  L0:41.5% L1:54.0% BI: 4.5%
[libx264 @ 0x2f4f7a0] final ratefactor: 21.45
[libx264 @ 0x2f4f7a0] 8x8 transform intra:67.5% inter:95.6%
[libx264 @ 0x2f4f7a0] coded y,uvDC,uvAC intra: 51.0% 93.4% 64.1% inter: 6.4% 28.0% 1.7%
[libx264 @ 0x2f4f7a0] i16 v,h,dc,p: 17% 46%  3% 35%
[libx264 @ 0x2f4f7a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 30% 13%  5%  5%  5%  7%  6%  6%
[libx264 @ 0x2f4f7a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 33%  7%  5%  8%  6%  8%  5%  4%
[libx264 @ 0x2f4f7a0] i8c dc,h,v,p: 37% 32% 18% 12%
[libx264 @ 0x2f4f7a0] Weighted P-Frames: Y:9.4% UV:5.9%
[libx264 @ 0x2f4f7a0] ref P L0: 88.1%  5.2%  5.7%  1.0%  0.0%
[libx264 @ 0x2f4f7a0] ref B L0: 96.4%  3.6%
[libx264 @ 0x2f4f7a0] ref B L1: 96.3%  3.7%
[libx264 @ 0x2f4f7a0] kb/s:824.63