*
* Each element has a state (see #GstState). You can get and set the state
* of an element with gst_element_get_state() and gst_element_set_state().
- * To get a string representation of a #GstState, use
- * gst_element_state_get_name().
+ * Setting a state triggers a #GstStateChange. To get a string representation
+ * of a #GstState, use gst_element_state_get_name().
*
* You can get and set a #GstClock on an element using gst_element_get_clock()
* and gst_element_set_clock().
*
* This function returns %GST_STATE_CHANGE_NO_PREROLL if the element
* successfully changed its state but is not able to provide data yet.
- * This mostly happens for live sources that only produce data in the PLAYING
- * state. While the state change return is equivalent to
+ * This mostly happens for live sources that only produce data in
+ * %GST_STATE_PLAYING. While the state change return is equivalent to
* %GST_STATE_CHANGE_SUCCESS, it is returned to the application to signal that
* some sink elements might not be able to complete their state change because
* an element is not producing data to complete the preroll. When setting the
/* gstmessage.h needs State */
/**
* GstState:
- * @GST_STATE_VOID_PENDING : no pending state.
- * @GST_STATE_NULL : the NULL state or initial state of an element
- * @GST_STATE_READY : the element is ready to go to PAUSED
- * @GST_STATE_PAUSED : the element is PAUSED
- * @GST_STATE_PLAYING : the element is PLAYING
- *
- * The posible states an element can be in.
+ * @GST_STATE_VOID_PENDING: no pending state.
+ * @GST_STATE_NULL : the NULL state or initial state of an element.
+ * @GST_STATE_READY : the element is ready to go to PAUSED.
+ * @GST_STATE_PAUSED : the element is PAUSED, it is ready to accept and
+ * process data. Sink elements however only accept one
+ * buffer and then block.
+ * @GST_STATE_PLAYING : the element is PLAYING, the #GstClock is running and
+ * the data is flowing.
+ *
+ * The posible states an element can be in. States can be chaged using
+ * gst_element_set_state() and checked using gst_element_get_state().
*/
typedef enum {
GST_STATE_VOID_PENDING = 0,
* @GST_STATE_CHANGE_SUCCESS : the state change succeeded
* @GST_STATE_CHANGE_ASYNC : the state change will happen asynchronously
* @GST_STATE_CHANGE_NO_PREROLL: the state change succeeded but the element
- * cannot produce data in PAUSED. This typically
- * happens with live sources.
+ * cannot produce data in %GST_STATE_PAUSED.
+ * This typically happens with live sources.
*
* The possible return values from a state change function. Only
* @GST_STATE_CHANGE_FAILURE is a real failure.
/**
* GstStateChange:
- * @GST_STATE_CHANGE_NULL_TO_READY : state change from NULL to READY
- * @GST_STATE_CHANGE_READY_TO_PAUSED : state change from READY to PAUSED
- * @GST_STATE_CHANGE_PAUSED_TO_PLAYING: state change from PAUSED to PLAYING
- * @GST_STATE_CHANGE_PLAYING_TO_PAUSED: state change from PLAYING to PAUSED
- * @GST_STATE_CHANGE_PAUSED_TO_READY : state change from PAUSED to READY
- * @GST_STATE_CHANGE_READY_TO_NULL : state change from READY to NULL
- *
- * The different (interesting) state changes that are passed to the
- * state change functions of elements.
+ * @GST_STATE_CHANGE_NULL_TO_READY : state change from NULL to READY.
+ * <itemizedlist>
+ * <listitem><para>
+ * The element must check if the resources it needs are available. Device
+ * sinks and -sources typically try to probe the device to constrain their
+ * caps.
+ * </para></listitem>
+ * <listitem><para>
+ * The element opens the device (in case feature need to be probed).
+ * </para></listitem>
+ * </itemizedlist>
+ * @GST_STATE_CHANGE_READY_TO_PAUSED : state change from READY to PAUSED.
+ * <itemizedlist>
+ * <listitem><para>
+ * The element pads are activated in order to receive data in PAUSED.
+ * Streaming threads are started.
+ * </para></listitem>
+ * <listitem><para>
+ * Some elements might need to return ASYNC and complete the state change
+ * when they have enough information. It is a requirement for sinks to
+ * return ASYNC and complete the state change when they receive the first
+ * buffer or EOS event (preroll). Sinks also block the dataflow when in
+ * PAUSED.
+ * </para></listitem>
+ * <listitem><para>
+ * A pipeline resets the running_time to 0.
+ * </para></listitem>
+ * <listitem><para>
+ * Live sources return NO_PREROLL and don't generate data.
+ * </para></listitem>
+ * </itemizedlist>
+ * @GST_STATE_CHANGE_PAUSED_TO_PLAYING: state change from PAUSED to PLAYING.
+ * <itemizedlist>
+ * <listitem><para>
+ * Most elements ignore this state change.
+ * </para></listitem>
+ * <listitem><para>
+ * The pipeline selects a clock and distributes this to all the children
+ * before setting them to PLAYING. This means that it is only alowed to
+ * synchronize on the clock in the PLAYING state.
+ * </para></listitem>
+ * <listitem><para>
+ * The pipeline uses the clock and the running_time to calculate the
+ * base_time. The base_time is distributed to all children when performing
+ * the state change.
+ * </para></listitem>
+ * <listitem><para>
+ * Sink elements stop blocking on the preroll buffer or event and start
+ * rendering the data.
+ * </para></listitem>
+ * <listitem><para>
+ * Sinks can post the EOS message in the PLAYING state. It is not allowed to
+ * post EOS when not in the PLAYING state.
+ * </para></listitem>
+ * <listitem><para>
+ * While streaming in PAUSED or PLAYING elements can create and remove
+ * sometimes pads.
+ * </para></listitem>
+ * <listitem><para>
+ * Live sources start generating data and return SUCCESS.
+ * </para></listitem>
+ * </itemizedlist>
+ * @GST_STATE_CHANGE_PLAYING_TO_PAUSED: state change from PLAYING to PAUSED.
+ * <itemizedlist>
+ * <listitem><para>
+ * Most elements ignore this state change.
+ * </para></listitem>
+ * <listitem><para>
+ * The pipeline calculates the running_time based on the last selected clock
+ * and the base_time. It stores this information to continue playback when
+ * going back to the PLAYING state.
+ * </para></listitem>
+ * <listitem><para>
+ * Sinks unblock any clock wait calls.
+ * </para></listitem>
+ * <listitem><para>
+ * When a sink does not have a pending buffer to play, it returns ASYNC from
+ * this state change and completes the state change when it receives a new
+ * buffer or an EOS event.
+ * </para></listitem>
+ * <listitem><para>
+ * Any queued EOS messages are removed since they will be reposted when going
+ * back to the PLAYING state. The EOS messages are queued in GstBins.
+ * </para></listitem>
+ * <listitem><para>
+ * Live sources stop generating data and return NO_PREROLL.
+ * </para></listitem>
+ * </itemizedlist>
+ * @GST_STATE_CHANGE_PAUSED_TO_READY : state change from PAUSED to READY.
+ * <itemizedlist>
+ * <listitem><para>
+ * Sinks unblock any waits in the preroll.
+ * </para></listitem>
+ * <listitem><para>
+ * Elements unblock any waits on devices
+ * </para></listitem>
+ * <listitem><para>
+ * Chain or get_range functions return WRONG_STATE.
+ * </para></listitem>
+ * <listitem><para>
+ * The element pads are deactivated so that streaming becomes impossible and
+ * all streaming threads are stopped.
+ * </para></listitem>
+ * <listitem><para>
+ * The sink forgets all negotiated formats
+ * </para></listitem>
+ * <listitem><para>
+ * Elements remove all sometimes pads
+ * </para></listitem>
+ * </itemizedlist>
+ * @GST_STATE_CHANGE_READY_TO_NULL : state change from READY to NULL.
+ * <itemizedlist>
+ * <listitem><para>
+ * Elements close devices
+ * </para></listitem>
+ * <listitem><para>
+ * Elements reset any internal state.
+ * </para></listitem>
+ * </itemizedlist>
+ *
+ * These are the different state changes an element goes through.
+ * %GST_STATE_NULL ⇒ %GST_STATE_PLAYING is called an upwards state change
+ * and %GST_STATE_PLAYING ⇒ %GST_STATE_NULL a downwards state change.
*/
typedef enum /*< flags=0 >*/
{