gstreamer/docs/random/sources
Erik Walthinsen da03fde054 WARNING: Don't grab this updated unless you're really, REALLY sure.
Original commit message from CVS:
WARNING: Don't grab this updated unless you're really, REALLY sure.
WARNING: Wait for the next one.

Whole lotta changes here, including a few random bits:

examples/*/Makefile: updated to use `libtool gcc`, not just `gcc`
gst/
gstbuffer.h: updated to new flag style
gst.c, gstdebug.h: added new debugging for function ptrs
gstpipeline.c: set type of parent_class to the class, not the object
gstthread.c: ditto
plugins/
cdparanoia/cdparanoia.c: added an argument type, updated some defaults
cobin/spindentity.c: updated to new do/while loopfunction style
mp3encode/lame/gstlame.c: argument types, whole lotta lame options
tests/: various changes

Now, for the big changes:  Once again, the scheduling system has changed.
And once again, it broke a whole bunch of things.  The gist of the change
is that there is now a function pointer for gst_pad_push and gst_pad_pull,
instead of a hard-wired function.  Well, currently they are functions, but
that's for debugging purposes only, they just call the function pointer
after spewing lots of DEBUG().

This changed the GstPad structure a bit, and the GstPad API as well.
Where elements used to provide chain() and pull() functions, they provide
chain() and get() functions. gst_pad_set_pull[region]_function has been
changed to get_pad_set_get[region]_function.  This means all the elements
out there that used to have pull functions need to be updated.  The calls
to that function have been changed in the normal elements, but the names
of the functions passed is still _pull[region](), which is an aesthetic
issue more than anything.

As for what doesn't work yet, just about anything dealing with Connections
is hosed, meaning threaded stuff won't work.  This will be fixed about 12
hours from now, after I've slept, etc.  The simplefake.c test works in
both cothreaded and chained cases, but not much else will work due to the
Connection problem.  Needless to say, don't grab this unless you *need*
these features *now*, else wait to update this stuff until tomorrow.

I'm going to sleep now.
2000-12-16 10:18:09 +00:00

324 lines
11 KiB
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There are a number of different ways of coding a GstSrc. I'll try to
outline them and how the function here:
1a) Simple push-function based with single output
*------* *------
! ! !
! src !--->--! plugin
! ! !
*------* *------
This is the style that all the existing sources use. There is a single
output pad, and a _push function that's global to the whole element. The
_push function simply constructs buffers and pushes them out the pad.
Chained (current implementation):
bin src pad1 pad2 plugin
! (= pad1->peer)
gst_bin_iterate
!
! (find entry)
!
! gst_src_push
!---------------->!
! (create buffer)
!
! gst_pad_push
!---------------->!
!
! pad1->chainfunc (pad1->peer)
!------------------------------->!
! !
: :
(more chaining)
: :
!<-------------------------------!
!<----------------!
!<-----------------!
!
iteration ends
!
---
-
Typically this will be the/an entry into the Bin. The Bin's iterate
function simply calls the Src's _push function. When the _push function
pushes a buffer out it's pad, the chain function of the peer pad is
called, presumably causing a push out the other side of that element, and
eventually data gets to the other end. The stack unrolls, and the
iteration ends for that Src.
Cothreaded:
Again, the source would generally be an entry into the Bin. A loopfunc
will be constructed around it, which will simply loop calling the Src's
_push function as in the non-cothreaded case. When the _push function
pushes a buffer, it finds a pushfunc attached to the pad, drops the buffer
in the pen, and calls the pushfunc provided by the Bin. This causes a
switch to the next element, then the next, to the end, at which point a
buffer pull will travel back down the chain. The _push function gets
context and finishes, at which point the loopfunc wrapper simply calls it
again in the next iteration.
(current implementation):
bin cothread1 src pad1 pad2 cothread2 plugin
! (src) (= pad2->peer) (plugin)
gst_bin_iterate
!
! (first entry)
!
! cothread_switch
!---------------->!
! gst_src_push
!---------------->!
! (create buffer)
!
! gst_pad_push (pad1)
!
!--------------------!
! (fill bufpen)
!
! cothread switch
----------------------->!
! gst_pad_pull (pad2)
!
!<----------!
!
! (get buffer from bufpen)
!
!---------->!
! pad2->chainfunc
!------------->!
!
:
:
!<-------------!
! gst_pad_pull (pad2)
!<----------!
!
! (bufpen empty)
!<----------!
!<-------------------------------------! cothread switch
!<----------------!
!
iteration ends
!
:
:
!
next iteration
!
! cothread_switch
!---------------->!
! gst_src_push
!---------------->!
! (create buffer)
!
! gst_pad_push (pad1)
!
!--------------------!
! (fill bufpen)
!
! cothread switch
!---------->!
! (get buffer from bufpen)
!
!---------->!
! pad2->chainfunc
!------------->!
!
:
:
!<-------------!
! gst_pad_pull (pad2)
!<----------!
!
! (bufpen empty)
!<----------!
!<-------------------------------------! cothread switch
!<----------------!
!
iteration ends
!
:
-----------------------------------------------------------------------------------------------
1b) Simple push-function based with multiple output
Chained:
Similar to the single output variant, except several chains are spawned
off, one per push, hanging off whichever pad the buffer is pushed off of.
The stack will grow and unwind as many times as buffers are pushed out.
(current implementation)
bin src pad1 pad2 plugin
! (= pad1->peer)
gst_bin_iterate
!
! (find entry)
!
! gst_src_push
!---------------->!
! (create buffer)
!
! gst_pad_push
!---------------->!
!
! pad1->chainfunc (pad1->peer)
!------------------------------->!
! !
: :
(more chaining)
: :
!<-------------------------------!
!<----------------!
! (create buffer)
!
! gst_pad_push
!---------------->!
!
! pad1->chainfunc (pad1->peer)
!------------------------------->!
! !
: :
(more chaining)
: :
!<-------------------------------!
!<----------------!
:
(more pushes)
:
!<-----------------!
!
iteration ends
!
---
-
Cothreaded:
Also similar to the single output variant. When the pull winds its way
back from the first push, execution returns to the Src's _push function,
which simply goes off and pushes out another buffer, causing another
series of context switches. Eventually the loopfunc wrapper starts over,
round and round we go.
-----------------------------------------------------------------------------------------------
2) Pull-function based with single output
Similar to a regular filter with a chain function associated with each
pad, this kind of source doesn't provide a src-wide push function, but
does provide pullfuncs for its pad. A pullfunc puts a buffer in the pen
and exits.
Chained:
bin src pad1 pad2 plugin
! (= pad1->peer)
gst_bin_iterate
!
! (find entry)
!
! (find src pad
! of entry element)
!
! gst_pad_pull
!------------------------------------------------>!
? !
!<------------------------------!
!
! (create buffer)
!
! gst_pad_push
!------------------------------>!
! (bufpen filled)
(return buffer) !
!<------------------------------------------------!
!
! gst_pad_chain
!------------------------------------------------------------------->!
!
:
(more chaining)
:
!<-------------------------------------------------------------------!
!
iteration ends
!
---
-
As usual, is likely to be an entry into a Bin. The Bin iterate code must
explicitely pull a buffer and pass it on to the peer.
Cothreaded:
bin cothread1 src pad1 pad2 cothread2 plugin
! (src) (= pad2->peer) (plugin)
gst_bin_iterate
!
! (first entry)
!
! cothread_switch
!---------------->! gst_pad_pull
!------------------------------------------------>!
? !
!<------------------------------!
!
! (create buffer)
!
! gst_pad_push
!------------------------------>!
! (bufpen filled)
(return buffer) !
!<------------------------------------------------!
!
! pad_chain
!--------------------------------------! cothread switch
|---------------------->!
! gst_pad_pull (pad2)
!
!<----------!
!
! (get buffer from bufpen)
!
!---------->!
! pad2->chainfunc
!------------->!
!
:
:
!<-------------!
! gst_pad_pull (pad2)
!<----------!
!
! (bufpen empty)
!<-----------!
! cothread switch
!-------------------!
!<----------------!
!<----------------!
!
iteration ends
!
: