title: ffmpeg mp4 video is not playing on html5 video player on browser (corrupt format)
body: <p>I am executing the following command to insert a watermark on the video and output as a mp4 format but that format is not playing on the browser by html5 video player.</p>
  
  <pre><code>$video_url = '../../../uploads/myvideo.mp4';
  $watermarked = '../../../uploads/watermarked_video.mp4';
  exec("ffmpeg -i $video_url -vf \"movie='sos.png', crop=iw:ih:0:0:dar [img]; [in] [img] overlay=(W-w)/2:(H-h)/2 [out]\" -vcodec mpeg4 -f avi $watermarked");  //creating water marked video
  </code></pre>
  
  <p>if i download it to my local machine then its playing perfectly on the player.</p>
  
  <p>is there any syntax problem?</p>