[FFmpeg-user] FFMPEG sidechaincompress not working as it should?

[Frank @ Taapo]

I have been trying to get sidechaining to work with FFMPEG, but my complex
filter skills are lacking.

I'm running two aif files into ffmpeg, hoping the voice would "duck" the
background music when the voice-over is speaking. But I get an error with
this command-line (on Windows, with latest FFMPEG binary):

ffmpeg.exe -i temp_music.aif -i temp_voice.aif -filter_complex
"[1:a]asplit=2[sc][mix];[0:a][sc]sidechaincompress=threshold=0.1:ratio=5[bg];
[bg][mix]amerge[fin‌​al]" -map [final] final.mp3

Everything decodes fine:

ffmpeg version N-87353-g183fd30 Copyright (c) 2000-2017 the FFmpeg
developers
  built with gcc 7.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --enable-cuda
--enable-cuvid --enable-d3d11va --enable-dxva2 --enable-libmfx
--enable-nvenc --enable-avisynth --enable-bzlib --enable-fontconfig
--enable-frei0r --enable-gnutls --enable-iconv --enable-libass
--enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype
--enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug
--enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb
--enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp
--enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora
--enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc
--enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp
--enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid
--enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib
  libavutil      55. 76.100 / 55. 76.100
  libavcodec     57.106.101 / 57.106.101
  libavformat    57. 82.101 / 57. 82.101
  libavdevice    57.  8.101 / 57.  8.101
  libavfilter     6.105.100 /  6.105.100
  libswscale      4.  7.103 /  4.  7.103
  libswresample   2.  8.100 /  2.  8.100
  libpostproc    54.  6.100 / 54.  6.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, aiff, from 'temp_music.aif':
  Duration: 00:01:26.68, start: 0.000000, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16be, 48000 Hz, stereo, s16, 1536 kb/s
Guessed Channel Layout for Input Stream #1.0 : stereo
Input #1, aiff, from 'temp_voice.aif':
  Duration: 00:01:26.68, start: 0.000000, bitrate: 1536 kb/s
    Stream #1:0: Audio: pcm_s16be, 48000 Hz, stereo, s16, 1536 kb/s
Output with label 'final' does not exist in any defined filter graph, or
was already used elsewhere.

But then I receive an error:

Output with label 'final' does not exist in any defined filter graph, or
was already used elsewhere.

Anybody knows why?
ᐧ