ffmpeg -i sfx_003.spc -acodec pcm_u8 -ar 44100 sfx_003.wav
ffmpeg version N-86862-g1b00600 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.3)
  configuration: --prefix=/home/blimpse/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/blimpse/ffmpeg_build/include --extra-ldflags=-L/home/blimpse/ffmpeg_build/lib --bindir=/home/blimpse/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree
  libavutil      55. 69.100 / 55. 69.100
  libavcodec     57.102.100 / 57.102.100
  libavformat    57. 76.100 / 57. 76.100
  libavdevice    57.  7.100 / 57.  7.100
  libavfilter     6. 95.100 /  6. 95.100
  libswscale      4.  7.101 /  4.  7.101
  libswresample   2.  8.100 /  2.  8.100
  libpostproc    54.  6.100 / 54.  6.100
sfx_003.spc: Invalid data found when processing input