Commit 790e5d10 authored by Stefan Kost's avatar Stefan Kost
Browse files

docs: add more docs around GstState and GstStateChange

Take reviewed docs from docs/design/part-state to have that more prominent
inside the api docs. Add a few sentences to link things better together.
parent f65a81ae
......@@ -56,8 +56,8 @@
*
* 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().
......@@ -2063,8 +2063,8 @@ interrupted:
*
* 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
......
......@@ -31,13 +31,17 @@ typedef struct _GstElementClass GstElementClass;
/* 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,
......@@ -78,8 +82,8 @@ G_BEGIN_DECLS
* @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.
......@@ -173,15 +177,129 @@ typedef enum {
/**
* 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 &rArr; %GST_STATE_PLAYING is called an upwards state change
* and %GST_STATE_PLAYING &rArr; %GST_STATE_NULL a downwards state change.
*/
typedef enum /*< flags=0 >*/
{
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment