Query
-----

Queries are used to get information about the state of the stream.
Various queries exist such as get the total length and the position

A query can be performed on a pad or on an element. Both the element
and the pad query have default behaviour unless a custom query handler
is installed.

The default pad query handler will forward the query to an internally
linked pad. This internally linked pad is either obtained by calling
the internal_links function of the pad or by using the default 
function (which selects the pads with oposite directions from the parent
element).

The default element query function will select a random source pad to
send the event to.

The pad query function has the following prototype:

    gboolean (*GstPadQueryFunction) (GstPad *pad, GstQueryType type,
                                     GstFormat *format, gint64  *value);

The query function can return a single value in one of the defined
formats.

The function returns TRUE if the query could be performed. The returned
values are undefined when this function returns FALSE.


Query types
-----------

 GST_QUERY_TOTAL:

   get the total length of the stream in the given format.

 GST_QUERY_POSITION:

   get the current position in the stream in the given format.

 GST_QUERY_LATENCY:

   get the latency introduced in the stream in the given format.
   This query can be used to retrieve how much data is queued in a
   queue or in a hardware device such as an audio sink.

 GST_QUERY_JITTER:

   Get the jitter, this is the difference between the expected and real
   time a buffer is captured or played.

 GST_QUERY_START:

   Query the position in the stream where the last start position was
   configured. When a seek was performed to play a stream from A to B,
   this query will return A.

 GST_QUERY_SEGMENT_END:

   Query the position in the stream where the last end position was
   configured. When a seek was performed to play a stream from A to B,
   this query will return B.

 GST_QUERY_RATE:

   Query the current playback rate of the stream.