title: FFMPEG says "No such file or directory" when trying to convert image sequence
body: <p>From the shell, when I specify a sequence of images via <code>%d</code> in the input filename, FFMPEG insists "No such file or directory", despite evidence to the contrary. Looking online, I haven't managed to find any references to generating video from a sequence of images using FFMPEG where <code>%d</code> is not used, yet it seems to fail here.</p>
  
  <p>My images should be identified by FFMPEG from <code>img%06d.gif</code>. Issuing <code>ls img[0-9][0-9][0-9][0-9][0-9][0-9].gif</code> succeeds in the very same directory I issue the FFMPEG command.</p>
  
  <p>The command I use is:</p>
  
  <pre><code>ffmpeg  -i img%06d.gif -c:v libx264 -r 30 -pix_fmt yuv720p test.mp4
  </code></pre>
  
  <p>What could possibly be going wrong???</p>