mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-25 11:11:08 +00:00
46 lines
2.1 KiB
Text
46 lines
2.1 KiB
Text
push-pull
|
|
---------
|
|
|
|
Normally a source element will push data to the downstream element using
|
|
the gst_pad_push() method. The downstream peer pad will receive the
|
|
buffer in the Chain function. In the push mode, the source element is the
|
|
driving force in the pipeline as it initiates data transport.
|
|
|
|
It is also possible for an element to pull data from an upstream element.
|
|
The downstream element does this by calling gst_pad_pull_range() on one
|
|
of its sinkpads. In this mode, the downstream element is the driving force
|
|
in the pipeline as it initiates data transfer.
|
|
|
|
It is important that the elements are in the correct state to handle a
|
|
push() or a pull_range() from the peer element. For push() based elements
|
|
this means that all downstream elements should be in the correct state and
|
|
for pull_range() based elements this means the upstream elements should
|
|
be in the correct state.
|
|
|
|
Most sinkpads implement a chain function. This is the most common case.
|
|
sinkpads implementing a loop function will be the exception. Likewise
|
|
srcpads implementing a getrange function will be the exception.
|
|
|
|
|
|
state changes
|
|
~~~~~~~~~~~~~
|
|
|
|
The GstBin sets the state of all the sink elements. These are the elements
|
|
without source pads.
|
|
|
|
Setting the state on an element will first activate all the srcpads and then
|
|
the sinkpads. For each of the sinkpads, gst_pad_check_pull_range() is
|
|
performed. If the sinkpad supports a loopfunction and the peer pad returns TRUE
|
|
from the GstPadCheckPullRange function, then the peer pad is activated first as
|
|
it must be in the right state to handle a _pull_range(). Note that the
|
|
state change of the element is not yet performed, just the activate function
|
|
is called on the source pad. This means that elements that implement a
|
|
getrange function must be prepared to get their activate function called
|
|
before their state change function.
|
|
|
|
Elements that have multiple sinkpads that require all of them to operate
|
|
in the same mode (push/pull) can use the _check_pull_range() on all
|
|
their pads and can then remove the loop functions if one of the pads does
|
|
not support pull based mode.
|
|
|
|
|