Similar to de30de865cd, this allows to follow the flow of events as they
arrive to a pad rather than only when they are pushed to a peer.
The hook is installed in gst_pad_send_event_unchecked() instead of
gst_pad_send_event() because the latter is often omitted: that is the
case especifically in gst_pad_push_event_unchecked(), where most event
propagation occurs.
This patch also makes use of the new hooks in the log tracer to log the
begining and end of the send_event processing.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8330>
Commit de30de865cd added a hook for pad-chain-{pre,post} and
pad-chain-list-{pre,post}. As explained in that commit, hooking the
chain is helpful because it allows you to hook to buffer propagation in
both srcpads (pad-push) and sinkpads (pad-chain).
This patch uses the new hooks to log pad-chain in the log tracer.
Before, only pad-push was logged, so you could only follow the flow of
buffers through the srcpads.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8329>
This patch adds documentation to the 'log' tracer and amends the design
document of Tracers to replace a misleading example of the 'log' tracer
with a different example that uses tracer arguments with tracers that do
actually handle said arguments.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4153>
