title: How to extract image frames from a bagfile?
body: <p>I am using ROS hydro on Ubuntu 12.04. After using the command </p>
  
  <p><code>rosrun image_view extract_images _sec_per_frame:=0.01 image:={IMAGE_TOPIC_IN_BAGFILE}</code></p>
  
  <p>I'm having an error when executing</p>
  
  <p><code>ffmpeg -r -b -i frame%04d.jpg .avi</code></p>
  
  <p>The thing is <em>I am not seeing the sequence of images</em> after I play the bagfile.</p>
  
  <p>I ran </p>
  
  <pre><code>rosbag info 
  </code></pre>
  
  <p>to obtain the topic in the bag file but when I run </p>
  
  <pre><code>rosrun rqtgraph rqtgraph
  </code></pre>
  
  <p>the /extract_image frame node is there all by itself.</p>
  
  <p>When I follow the tutorials on <a href="http://wiki.ros.org/rosbag/Tutorials/" rel="nofollow">http://wiki.ros.org/rosbag/Tutorials/</a>... I get an error</p>
  
  <p><code>[FATAL] [1394583654.335465840]: Error opening file: play</code>.</p>
  
  <p>After replacing play by "-<strong>-clock</strong>" everything seemed to go just fine but there are no <strong>frames*.jpg</strong> in <strong><em>/home/.ros</em></strong> hence <em>the sequence of images are still missing</em>.</p>