gstreamer/docs/random/wtay/states

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1) transitions
--------------
There are four states, NULL, READY, PAUSED, PLAYING. state transitions only
happen from once neighbouring state to another.
NULL: the element is just being created, the initial state.
!
! the element creates all of its resources (a thread will create
! its pthread etc..)
! - most used by bins to set up thread context for its children
v
READY: the element is ready to start processing.
!
! the element sets up its state so it can start processing buffers.
! - open devices
v
PAUSED: the element is paused
!
! the element starts spinning
!
v
PLAYING: the element is playing
!
! the element stops spinning
! the element frees resources from other plugins (bufferpools)
!
v
PAUSED
! element removes caps from pads
! reset internal state
! - close devices
!
v
READY
!
! the element frees all of its resources (eg: pthread_join)
!
v
NULL
2) bin transition
-----------------
the state of a bin is equal to the maximum state of its children.
3) interaction with the scheduler
---------------------------------
elements in the !PLAYING state are disabled in the scheduler.
4) action that can be performed by the app in the different states
------------------------------------------------------------------
PLAYING: nothing, only iterate on the pipeline, some properties can
be changed.
PAUSED: elements can be connected, removed, disconnected. some
properties can be changed
READY: as in PAUSED but *all* properties can be changed.
NULL: everything.