When the link on the pipewire side is destroyed, on video streams, buffers
are removed abruptly and there is no way this pipeline can be revived,
so let's post an element error to stop it.
On a normal shutdown, the pool is first set to flushing in change_state(),
so checking for the flushing state is a good indicator to know if this
is a normal shutdown or not.
See #1980
This is for readability and better control.
Make sure we clear out all pointers to anything related to the released
pw_buffer, including all the memories.
Many Gstreamer elements support transforming buffers via the
`image-orientation` tag. Use it to implement support for the new
VideoTransform meta.
In order for Gstreamer pipelines to enable support for these tags
usually the rotate method has to be set to `auto` or `automatic`,
e.g. `videoflip method=automatic`, `glimagesink rotate-method=automatic`
or `waylandsink rotate-method=auto`.
Pipewire might update buffers that have not been recycled by GStreamer,
because they are still used downstream. There is nothing we can do about
it in the pipewiresrc.
If a buffer is sent downstream more than once, take an additional
reference to make sure that we don't queue a buffer that is still used
and print a warning.
Simplify the stream API. make just 2 methods to queue and dequeue
buffers. Make just one callback when new buffers can be dequeued.
Add support for driver nodes such as the video-src.
Pass a pw_buffer structure to add/remove_buffer and make it possible
to attach metadata to it. This makes it a lot easier to implement
the gstreamer pipewire pool.
Call the stream process function from the main loop and use a lockfree
ringbuffer to pass buffers between the threads. Make it possible to
also call process from the RT thread.
unmap the buffer data when needed.
