title: ffmpeg: unable to merge valid mp4 and mp3 together
body: <p>I try to merge 2 files
  1 mp4 video + 1 mp3 files (both are ok and are playable inside chrome or firefox)</p>
  
  <pre><code>mediainfo yarek.mp4
  General
  Complete name                            : yarek.mp4
  Format                                   : MPEG-4
  Format profile                           : Base Media
  Codec ID                                 : isom (isom/iso2/avc1/mp41)
  File size                                : 86.7 KiB
  Duration                                 : 5 s 263 ms
  
  mediainfo yarek.mp3
  General
  Complete name                            : yarek.mp3
  Format                                   : MPEG Audio
  File size                                : 83.9 KiB
  Overall bit rate mode                    : Variable
  Writing library                          : Lavf57.56.101
  </code></pre>
  
  <p>I run: </p>
  
  <pre><code>ffmpeg -i yarek.mp4 -i yarek.mp3 output.mp4
  </code></pre>
  
  <p>Gives me that error:</p>
  
  <pre><code>buffer @ 0x55656c11b0e0] Unable to parse option value "-1" as pixel format
      Last message repeated 1 times
  [buffer @ 0x55656c11b0e0] Error setting option pix_fmt to value -1.
  [graph 0 input from stream 0:0 @ 0x55656c11aa40] Error applying options to the filter.
  </code></pre>
  
  <p>Same problem when I try to extract a JPEG form the mp4 (the mp4 is valid and can be opened within VLC or inside Chrome or Firefow)</p>
  
  <pre><code>/var/www/html/record# ffmpeg -y -i "yarek.mp4" -ss "1" -vframes 1 -q:v 2 output.jpg
  ffmpeg version 3.2.12-1~deb9u1 Copyright (c) 2000-2018 the FFmpeg developers
    built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
    configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
    libavutil      55. 34.101 / 55. 34.101
    libavcodec     57. 64.101 / 57. 64.101
    libavformat    57. 56.101 / 57. 56.101
    libavdevice    57.  1.100 / 57.  1.100
    libavfilter     6. 65.100 /  6. 65.100
    libavresample   3.  1.  0 /  3.  1.  0
    libswscale      4.  2.100 /  4.  2.100
    libswresample   2.  3.100 /  2.  3.100
    libpostproc    54.  1.100 / 54.  1.100
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x55d221642ee0] Missing key frame while reordering index according to edit list
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x55d221642ee0] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none, 640x480, 128 kb/s): unspecified pixel format
  Consider increasing the value for the 'analyzeduration' and 'probesize' options
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'yarek.mp4':
    Metadata:
      major_brand     : isom
      minor_version   : 512
      compatible_brands: isomiso2avc1mp41
      encoder         : Lavf57.56.101
      comment         : {"t": "v", "c": "h264", "s": 1543853355450975, "u": 1543853355472477}
    Duration: 00:00:22.73, bitrate: 130 kb/s
      Stream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 640x480, 128 kb/s, 14.69 fps, 15 tbr, 90k tbn, 180k tbc (default)
      Metadata:
        handler_name    : VideoHandler
  [buffer @ 0x55d221663420] Unable to parse option value "-1" as pixel format
      Last message repeated 1 times
  [buffer @ 0x55d221663420] Error setting option pix_fmt to value -1.
  [graph 0 input from stream 0:0 @ 0x55d221642d60] Error applying options to the filter.
  Error opening filters!
  </code></pre>