gstreamer/docs/manual/queues.sgml

<chapter id="cha-queues">
  <title>Queues</title>
  <para> 
    A <classname>GstQueue</classname> is a filter element.
    Queues can be used to connect two elements in such way that the data can 
    be buffered.
  </para>
  <para> 
    A buffer that is sinked to a Queue will not automatically be pushed to the
    next connected element but will be buffered. It will be pushed to the next
    element as soon as gst_connection_push () is called.
  </para>
  <para> 
    Queues are mostly used in conjunction with a <classname>GstThread</classname> to
    provide an external connection for the thread elements. You could have one
    thread feeding buffers into a <classname>GstQueue</classname> and another
    thread repeadedly calling gst_connection_push () on the queue to feed its 
    internal elements.
  </para>

  <para> 
    Below is a figure of a two-threaded decoder. We have one thread (the main execution
    thread) reading the data from a file, and another thread decoding the data.
  </para>
  <figure float="1" id="sec-queues-img">
    <title>a two-threaded decoder with a queue</title>
    <graphic fileref="images/queue" format="png"></graphic>
  </figure>



</chapter>