title: java.io.ioexception.Runtime.getRuntime().exec(). environment and working directory null error in android
body: <pre><code>File dir = new File("/mnt/sdcard");
  Process process = Runtime.getRuntime().exec("ffmpeg -f image2 -i img%4d.png video.mp4", null, dir);
  </code></pre>
  
  <p>when i try this line in android,i get environment and working directory null error in android. But when i try that line in java,it worked perfectly.but in android,it has some problem.</p>