title: how to mux audio and video in gstreamer
body: <p>I'm trying to mux a .ogv only video file
  with a .mp3 file to get a .ogv file with both video and audio, in gstreamer (v0.10). I try this pipeline :</p>
  
  <pre><code>gst-launch-0.10 filesrc location="video.ogv" ! oggdemux ! queue ! oggmux name=mux ! filesink location="test.ogv" filesrc location="audio.mp3" ! audioconvert ! vorbisenc ! queue ! mux.
  </code></pre>
  
  <p>When I use this command line, i get an error :</p>
  
  <pre><code>ERROR : of element /GstPipeline:pipeline0/GstAudioConvert:audioconvert0 : not negotiated
  Additional debogging information :
  gstbasetransform.c(2541): gst_base_transform_handle_buffer (): /GstPipeline:pipeline0/GstAudioConvert:audioconvert0:
  not negotiated
  ERROR : the pipeline refuse to pass in preparation phase
  </code></pre>
  
  <p>I can't see what's wrong. Any suggestion ?
  Thanks.</p>