Commit f7a7a569 authored by Sebastian Dröge's avatar Sebastian Dröge 🍵
Browse files

netclientclock: Filter RTTs based on the median of the last RTTs before considering them at all

This improves accuracy on wifi or similar networks, where the RTT can go very
high up for a single observation every now and then. Without filtering them
away completely, they would still still modify the average RTT, and thus all
clock estimations.
parent 42b16c9e
......@@ -60,6 +60,8 @@
#include <gio/gio.h>
#include <string.h>
GST_DEBUG_CATEGORY_STATIC (ncc_debug);
#define GST_CAT_DEFAULT (ncc_debug)
......@@ -74,6 +76,8 @@ GST_DEBUG_CATEGORY_STATIC (ncc_debug);
/* Maximum number of clock updates we can skip before updating */
#define MAX_SKIPPED_UPDATES 5
#define MEDIAN_PRE_FILTERING_WINDOW 9
enum
{
PROP_0,
......@@ -101,6 +105,8 @@ struct _GstNetClientClockPrivate
GstClockTime rtt_avg;
GstClockTime minimum_update_interval;
guint skipped_updates;
GstClockTime last_rtts[MEDIAN_PRE_FILTERING_WINDOW];
gint last_rtts_missing;
gchar *address;
gint port;
......@@ -195,6 +201,7 @@ gst_net_client_clock_init (GstNetClientClock * self)
priv->roundtrip_limit = DEFAULT_ROUNDTRIP_LIMIT;
priv->minimum_update_interval = DEFAULT_MINIMUM_UPDATE_INTERVAL;
priv->skipped_updates = 0;
priv->last_rtts_missing = MEDIAN_PRE_FILTERING_WINDOW;
}
static void
......@@ -307,6 +314,16 @@ gst_net_client_clock_get_property (GObject * object, guint prop_id,
}
}
static gint
compare_clock_time (const GstClockTime * a, const GstClockTime * b)
{
if (*a < *b)
return -1;
else if (*a > *b)
return 1;
return 0;
}
static void
gst_net_client_clock_observe_times (GstNetClientClock * self,
GstClockTime local_1, GstClockTime remote, GstClockTime local_2)
......@@ -327,6 +344,9 @@ gst_net_client_clock_observe_times (GstNetClientClock * self,
GstClockTime orig_internal_time, orig_external_time, orig_rate_num,
orig_rate_den;
GstClockTime max_discont;
GstClockTime last_rtts[MEDIAN_PRE_FILTERING_WINDOW];
GstClockTime median;
gint i;
GST_OBJECT_LOCK (self);
rtt_limit = self->priv->roundtrip_limit;
......@@ -351,6 +371,33 @@ gst_net_client_clock_observe_times (GstNetClientClock * self,
goto bogus_observation;
}
for (i = 1; i < MEDIAN_PRE_FILTERING_WINDOW; i++)
self->priv->last_rtts[i - 1] = self->priv->last_rtts[i];
self->priv->last_rtts[i - 1] = rtt;
if (self->priv->last_rtts_missing) {
self->priv->last_rtts_missing--;
} else {
memcpy (&last_rtts, &self->priv->last_rtts, sizeof (last_rtts));
g_qsort_with_data (&last_rtts,
MEDIAN_PRE_FILTERING_WINDOW, sizeof (GstClockTime),
(GCompareDataFunc) compare_clock_time, NULL);
median = last_rtts[MEDIAN_PRE_FILTERING_WINDOW / 2];
/* FIXME: We might want to use something else here, like only allowing
* things in the interquartile range, or also filtering away delays that
* are too small compared to the median. This here worked well enough
* in tests so far.
*/
if (rtt > 2 * median) {
GST_LOG_OBJECT (self,
"Dropping observation, long RTT %" GST_TIME_FORMAT " > 2 * median %"
GST_TIME_FORMAT, GST_TIME_ARGS (rtt), GST_TIME_ARGS (median));
goto bogus_observation;
}
}
/* Track an average round trip time, for a bit of smoothing */
/* Always update before discarding a sample, so genuine changes in
* the network get picked up, eventually */
......
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