mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-22 17:51:16 +00:00
Added a drawing of a possible player architecture added plugin guidelines
Original commit message from CVS: Added a drawing of a possible player architecture added plugin guidelines
This commit is contained in:
Wim Taymans
parent
02c10c5005
commit
93b782b643
2 changed files with 328 additions and 0 deletions
33
docs/random/wtay/player.fig
Normal file
33
docs/random/wtay/player.fig
Normal file
|
|
@ -0,0 +1,33 @@
|
|||
#FIG 3.2
|
||||
Landscape
|
||||
Center
|
||||
Metric
|
||||
A4
|
||||
100.00
|
||||
Single
|
||||
-2
|
||||
1200 2
|
||||
2 2 0 1 0 6 50 0 20 0.000 0 0 -1 0 0 5
|
||||
5895 3465 8460 3465 8460 5175 5895 5175 5895 3465
|
||||
2 2 0 1 0 7 50 0 -1 0.000 0 0 -1 0 0 5
|
||||
4905 1935 8640 1935 8640 5310 4905 5310 4905 1935
|
||||
2 2 0 1 0 7 50 0 -1 0.000 0 0 -1 0 0 5
|
||||
2610 1935 4815 1935 4815 5310 2610 5310 2610 1935
|
||||
2 2 0 1 0 7 50 0 -1 0.000 0 0 -1 0 0 5
|
||||
495 675 8685 675 8685 5400 495 5400 495 675
|
||||
2 2 0 1 0 7 50 0 -1 0.000 0 0 -1 0 0 5
|
||||
675 1935 2430 1935 2430 3465 675 3465 675 1935
|
||||
4 0 0 50 0 0 12 0.0000 4 180 615 6210 3915 GstPlay\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1485 6480 4455 - GStreamer (glib2)\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1470 5130 2250 Bonobo Component\001
|
||||
4 0 0 50 0 0 12 0.0000 4 135 1275 5130 2700 - sliders/buttons\001
|
||||
4 0 0 50 0 0 12 0.0000 4 135 1260 5130 2925 - Gtk/Gnome etc\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1245 5130 3150 - uses libgstplay\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1095 2700 945 GstMediaPlay\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1785 2745 1170 - app using components\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1440 2700 2160 Bonobo component\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1035 2700 2610 - playlist etc..\001
|
||||
4 0 0 50 0 0 12 0.0000 4 180 1395 855 2160 Other components\001
|
||||
4 0 0 50 0 0 12 0.0000 4 135 705 855 2610 - encoder\001
|
||||
4 0 0 50 0 0 12 0.0000 4 135 540 855 2835 - editor\001
|
||||
4 0 0 50 0 0 12 0.0000 4 60 240 855 3060 - ...\001
|
||||
295
docs/random/wtay/plugin_guidelines
Normal file
295
docs/random/wtay/plugin_guidelines
Normal file
|
|
@ -0,0 +1,295 @@
|
|||
|
||||
This short document gives some guidelines to plugin writers.
|
||||
|
||||
|
||||
chain-based plugins
|
||||
===================
|
||||
|
||||
- the plugin has a chain function on each sink pad (can be the same function)
|
||||
|
||||
!
|
||||
! chain (GstPad *pad, GstBuffer *buffer)
|
||||
! {
|
||||
! MyElement *elem = MY_ELEMENT (gst_pad_get_parent (pad));
|
||||
! GstBuffer *new_buffer;
|
||||
!
|
||||
! ...
|
||||
! (process the buffer)
|
||||
! ...
|
||||
!
|
||||
! /* you can push as many buffers (0 or more) as you want */
|
||||
! while (!done) {
|
||||
! ...
|
||||
! (process some more
|
||||
! ...
|
||||
! gst_pad_push (elem->some_sink_pad, new_buffer);
|
||||
! ...
|
||||
! /* if you're like going to send a large amount of buffers
|
||||
! * it's a good idea to call _yield from time to time after
|
||||
! * the buffer has been pushed */
|
||||
! (optional gst_element_yield (GST_ELEMENT (elem)); )
|
||||
! }
|
||||
! }
|
||||
!
|
||||
|
||||
- chain based functions are usually easy and recommended.
|
||||
- use gst_element_yield if you are going to push a lot of buffers.
|
||||
|
||||
|
||||
|
||||
loop-based plugins
|
||||
==================
|
||||
|
||||
- one loop function for the element.
|
||||
- required for bytestream based plugins.
|
||||
|
||||
simple case
|
||||
-----------
|
||||
|
||||
- one pull at the start
|
||||
|
||||
- if you do something like this, you really should consider using a
|
||||
chain function as it can be significantly optimised by the scheduler.
|
||||
|
||||
!
|
||||
! loop (GstElement *element)
|
||||
! {
|
||||
! MyElement *elem = MY_ELEMENT (element);
|
||||
! GstBuffer *buffer;
|
||||
! GstBuffer *new_buffer;
|
||||
!
|
||||
! buffer = gst_pad_pull (elem->sinkpad);
|
||||
!
|
||||
! ...
|
||||
! (do something)
|
||||
! ...
|
||||
!
|
||||
! /* you can push as many buffers (0 or more) as you want */
|
||||
! while (!done) {
|
||||
! ...
|
||||
! (process some more
|
||||
! ...
|
||||
! gst_pad_push (elem->some_sink_pad, new_buffer);
|
||||
! ...
|
||||
! /* if you're like going to send a large amount of buffers
|
||||
! * it's a good idea to call _yield from time to time after
|
||||
! * the buffer has been pushed */
|
||||
! (optional gst_element_yield (GST_ELEMENT (elem)); )
|
||||
! }
|
||||
! }
|
||||
!
|
||||
|
||||
DONT!!
|
||||
|
||||
- infinite loop
|
||||
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
! while (TRUE) {
|
||||
! ...
|
||||
! _pull ()
|
||||
! ...
|
||||
!
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
! }
|
||||
! }
|
||||
!
|
||||
|
||||
* you can fix this by either:
|
||||
|
||||
- setting the GST_ELEMENT_INFINITE_LOOP flag on the element. this is
|
||||
not recommended, if all plugins in the pipeline (or depending on the
|
||||
pipeline, some plugins) have this flag, the pipeline will not run.
|
||||
- calling break; from time to time to get out of the loop. (duh, then
|
||||
it's not an infinite loop anymore). beware that the next time the loop
|
||||
function is called, it will be started from the top.
|
||||
- calling gst_element_yield() from time to time (see NOTES).
|
||||
- this is fine (albeit rather useless, use a chain function):
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
! ...
|
||||
! _pull ()
|
||||
! ...
|
||||
!
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
! }
|
||||
!
|
||||
- so is this (albeit rather useless, consider removing the while and the _yield):
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
! while (TRUE) {
|
||||
! ...
|
||||
! _pull ()
|
||||
! ...
|
||||
!
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
! gst_element_yield (element);
|
||||
! }
|
||||
! }
|
||||
!
|
||||
|
||||
|
||||
DONT!!
|
||||
|
||||
- allocate data, loop, free data
|
||||
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
!
|
||||
! (my funky malloc)
|
||||
!
|
||||
! while (TRUE) {
|
||||
!
|
||||
! ...
|
||||
! _pull ()
|
||||
! ...
|
||||
!
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
!
|
||||
! _yield ()
|
||||
! }
|
||||
!
|
||||
! (my funky free)
|
||||
!
|
||||
! }
|
||||
!
|
||||
|
||||
- the free will NEVER happen!.
|
||||
|
||||
* You can fix this by:
|
||||
|
||||
- allocating/freeing data in the state change function
|
||||
- you could think the following code would work too:
|
||||
!
|
||||
! (*WRONG* example follows)
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
!
|
||||
! (my funky malloc)
|
||||
!
|
||||
! while (TRUE) {
|
||||
!
|
||||
! ...
|
||||
! _pull ()
|
||||
! if (EOS)
|
||||
! break;
|
||||
!
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
!
|
||||
! _yield ()
|
||||
! }
|
||||
!
|
||||
! (my funky free)
|
||||
!
|
||||
! }
|
||||
!
|
||||
but it'll only free the data if the pipeline was shut down with
|
||||
and EOS so don't try it. Besides, on EOS, a state change will happen
|
||||
anyway so free the data there.
|
||||
|
||||
|
||||
bytestream/multiple pull case
|
||||
-----------------------------
|
||||
|
||||
- same as the simple case, but you can't use a chain based function unless
|
||||
you want to make things a little harder then they should be.
|
||||
|
||||
|
||||
complicated case
|
||||
----------------
|
||||
|
||||
- push and pull are completely mixed.
|
||||
- the flow is usually something like this:
|
||||
|
||||
!
|
||||
! loop (element)
|
||||
! {
|
||||
!
|
||||
! while (TRUE) {
|
||||
!
|
||||
! while (something) {
|
||||
! ...
|
||||
! do some _pull ()
|
||||
! ...
|
||||
! do some _push ()
|
||||
! ...
|
||||
! while (something_else) {
|
||||
! ...
|
||||
! if (testing)
|
||||
! do some _pull ()
|
||||
! ...
|
||||
! do some _push ()
|
||||
! }
|
||||
! }
|
||||
!
|
||||
! while (something_useful) {
|
||||
! ...
|
||||
! _push ()
|
||||
! ...
|
||||
! }
|
||||
! }
|
||||
! }
|
||||
!
|
||||
(example made complicated on purpose, but vorbisdec comes close)
|
||||
|
||||
- you cannot call break to avoid infinite loops and there are loops that
|
||||
take a significant amount of time to execute, possibly pushing/pulling
|
||||
a lot of buffers.
|
||||
|
||||
* You can fix this by:
|
||||
|
||||
- inserting gst_element_yield () in sane places, don't exagerate because
|
||||
every yield can potentially never return so you need to keep track of
|
||||
allocations (see the NOTES below).
|
||||
|
||||
|
||||
|
||||
NOTES:
|
||||
======
|
||||
|
||||
- a call to _yield() can never return. if you have data allocated on the
|
||||
stack before the yield, keep a pointer to it in the element struct
|
||||
and free it in the state change function.
|
||||
|
||||
|
||||
IMPLEMENATION DETAILS
|
||||
=====================
|
||||
|
||||
The infinite loops are only problematic if the scheduler chooses to select
|
||||
the plugin as an entry point in the chain. _yield() will be a nop if this is
|
||||
not the case. The scheduler will not select plugins with the INFINITE_LOOP
|
||||
flag set as entries in a chain.
|
||||
|
||||
A _yield in an entry will hand over control to the main thread context, allowing
|
||||
state changes and other actions to be performed. It will basically exit the
|
||||
_iterate() function. spending a long time in a loop will degrade app responsiveness
|
||||
because _iterate will take a long time.
|
||||
|
||||
Calling yield, pulling, pushing can potentially never return because a state change
|
||||
might have happened, killing off execution of the plugin. pulling/pushing buffers
|
||||
will cause no leaks in this case because the core will free pending buffers in a
|
||||
state change to READY. The plugin must free allocated data/buffers itself in the state
|
||||
change function if the yield didn't retrun.
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Loading…
Reference in a new issue