The src can listen to RequestProcess commands and so gets the
node.supports-request = 1 property.
The play-pull example can both be a driver that listens to
RequestProcess or a lazy driver so set this in properties as well.
We can now remove the priority.driver property because automatic
priority selection will make us a driver or not.
With this change, video-src to video-play-pull will use lazy scheduling
with play-pull as the driver. video-play-pull to v4l2src will use
normal scheduling and video-src to video-play will also use normal
scheduling.
Make the alignment parameter optional when negotiating buffers.
Default to a 16 bytes alignment and adjust for the max cpu
alignment.
Remove the useless align buffer parameter in plugins, we always
set it to 16 anyway.
Let video-src unconditionally call _trigger_process() when it is
ready. This will either start the graph when it is the driver or emit
a RequestProcess event to the driver.
Let video-play-pull intercept the RequestProcess command and use it
to do a trigger_process(). Otherwise use a timer to pull in the next
frame.
It has the DRIVER flag set and sets a PW_KEY_PRIORITY_DRIVER value
to something higher than the source so that it becomes the driver.
Every timeout it does pw_stream_drive() to start the graph, which
will eventually call the process function with a pulled buffer to
display.
The framerate is set to something lower (80ms between frames) to
show the pull effect.
fixes#1484
