ffmpeg version 4.0.2-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100
[mp3 @ 0x5111bc0] invalid concatenated file detected - using bitrate for duration
[mp3 @ 0x5111bc0] Estimating duration from bitrate, this may be inaccurate
Input #0, mp3, from 'concat:./1.mp3|./2.mp3':
  Duration: 00:00:03.11, start: 0.050113, bitrate: 64 kb/s
    Stream #0:0: Audio: mp3, 22050 Hz, mono, fltp, 64 kb/s
    Metadata:
      encoder         : LAME3.99r
    Side data:
      replaygain: track gain - -10.600000, track peak - unknown, album gain - unknown, album peak - unknown,
Output #0, mp3, to './3.mp3':
  Metadata:
    TSSE            : Lavf58.12.100
    Stream #0:0: Audio: mp3, 22050 Hz, mono, fltp, 64 kb/s
    Metadata:
      encoder         : LAME3.99r
    Side data:
      replaygain: track gain - -10.600000, track peak - unknown, album gain - unknown, album peak - unknown,
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=      25kB time=00:00:03.03 bitrate=  66.3kbits/s speed=6.92e+03x
video:0kB audio:24kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.017454%