Previously, with opportunistic sync we'd track a master
clock as soon as we see a SYNC message, and hence sync up
faster, but then we'd announce we're synched before seeing
the ANNOUNCE, leaving the clock details like grandmaster-clock
empty.
A better way is to start tracking the clock opportunistically,
but not announce we're synched until we've also seen the ANNOUNCE.
The follow-up and delay-resp messages carry precise
timestamps for the arrival at the clock master, but
the local return time is unimportant, so we should be very
lenient in accepting them late. Some PTP masters don't
prioritise sending those packets, and we reject all the
responses and never sync - or take forever to do so.
Increase the tolerance to 20x the mean path delay.
Also fix a typo in one debug output that would print
the absolute time of the delay-resp message, not the offset
from the delay-req that it's actually being compared against.
The gst_ptp_clock_new() does not actually require a name. However, for
example the rtpjitterbuffer may create a clock without a name, fail, and
fall back to not using the PTP clock.
https://bugzilla.gnome.org/show_bug.cgi?id=791034
This is something bindings can't handle and it causes leaks. Instead
move the ref_sink() to the explicit, new() constructors.
This means that abstract classes, and anything that can have subclasses,
will have to do ref_sink() in their new() function now. Specifically
this affects GstClock and GstControlSource.
https://bugzilla.gnome.org/show_bug.cgi?id=743062
They don't necessarily use the same underlying clocks (e.g. on Windows), or
might be configured to a different clock type (monotonic vs. real time clock).
We need the values a clean system clock returns, as those are the values used
by the internal clocks.
If the delay measurement is too far away from the median of the window of last
delay measurements, we discard it. This increases accuracy on wifi a lot.
https://bugzilla.gnome.org/show_bug.cgi?id=749391
We should do some more measurements with all these and check how much sense
they make for PTP. Also enabling them means not following IEEE1588-2008 by the
letter anymore.
https://bugzilla.gnome.org/show_bug.cgi?id=749391
GstPtpClock implements a PTP (IEEE1588:2008) ordinary clock in
slave-only mode, that allows a GStreamer pipeline to synchronize
to a PTP network clock in some specific domain.
The PTP subsystem can be initialized with gst_ptp_init(), which then
starts a helper process to do the actual communication via the PTP
ports. This is required as PTP listens on ports < 1024 and thus
requires special privileges. Once this helper process is started, the
main process will synchronize to all PTP domains that are detected on
the selected interfaces.
gst_ptp_clock_new() then allows to create a GstClock that provides the
PTP time from a master clock inside a specific PTP domain. This clock
will only return valid timestamps once the timestamps in the PTP domain
are known. To check this, the GstPtpClock::internal-clock property and
the related notify::clock signal can be used. Once the internal clock
is not NULL, the PTP domain's time is known. Alternatively you can wait
for this with gst_ptp_clock_wait_ready().
To gather statistics about the PTP clock synchronization,
gst_ptp_statistics_callback_add() can be used. This gives the
application the possibility to collect all kinds of statistics
from the clock synchronization.
https://bugzilla.gnome.org/show_bug.cgi?id=749391
