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