title: ffmpeg cannot concatenate m4a files with -c copy parameter
body: <p>While using <strong>ffmpeg</strong> to concatenate similar <strong>m4a</strong> files:</p>
  
  <pre><code>ffmpeg -f concat -safe 0 -i &lt;(for f in ./*.m4a; do echo "file '$PWD/$f'"; done) -c copy output.m4a
  </code></pre>
  
  <p><strong>ffmpeg</strong> reports an error:</p>
  
  <pre><code>[ipod @ 0x7f8db8014a00] Could not find tag for codec mjpeg in stream #0, codec not currently supported in container
  </code></pre>
  
  <p>Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument</p>
  
  <p>The files used are: <code>chapter1.m4a</code>, <code>chapter2.m4a</code>. Their <strong>ffprobe</strong> have no differences other than the duration. Possible related output is:</p>
  
  <pre><code>Duration: 00:13:16.72, start: 0.000000, bitrate: 48 kb/s
  Stream #0:0(eng): Audio: aac (HE-AAC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 46 kb/s (default)
  Metadata:
    handler_name    : SoundHandler
  Stream #0:1: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 640x360 [SAR 100:100 DAR 16:9], 90k tbr, 90k tbn, 90k tbc
  </code></pre>