From: Steinar H. Gunderson <steinar+nageru@gunderson.no>
Date: Sun, 30 Aug 2020 22:25:40 +0000 (+0200)
Subject: Reset jitter history when frame rate changes.
X-Git-Tag: 2.0.2~13
X-Git-Url: https://git.sesse.net/?p=nageru;a=commitdiff_plain;h=ccc8294ad233bf3b85545c15c63100d54e485e63

Reset jitter history when frame rate changes.

This is seemingly especially important when we have input format autodetect
and PAL input rates; it gives us one 59.97 fps frame, then a delay as the
card autodetects and resyncs (might be as much as 30–50 ms; not entirely sure),
and then a steady stream of 50 fps frames. This then causes us to overestimate
the jitter by a lot until we get more than 1000 frames and can reject that
very first event as the outlier it is.
---

diff --git a/nageru/mixer.cpp b/nageru/mixer.cpp
index 2fdbf64..ce8a732 100644
--- a/nageru/mixer.cpp
+++ b/nageru/mixer.cpp
@@ -234,6 +234,16 @@ void JitterHistory::unregister_metrics(const vector<pair<string, string>> &label
 
 void JitterHistory::frame_arrived(steady_clock::time_point now, int64_t frame_duration, size_t dropped_frames)
 {
+	if (frame_duration != last_duration) {
+		// If the frame rate changed, the input clock is also going to change,
+		// so our historical data doesn't make much sense anymore.
+		// Also, format changes typically introduce blips that are not representative
+		// of the typical frame stream. (We make the assumption that format changes
+		// don't happen all the time in regular use; if they did, we should probably
+		// rather keep the history so that we take jitter they may introduce into account.)
+		clear();
+		last_duration = frame_duration;
+	}
 	if (expected_timestamp > steady_clock::time_point::min()) {
 		expected_timestamp += dropped_frames * nanoseconds(frame_duration * 1000000000 / TIMEBASE);
 		double jitter_seconds = fabs(duration<double>(expected_timestamp - now).count());
diff --git a/nageru/queue_length_policy.h b/nageru/queue_length_policy.h
index 329eb82..0b8a420 100644
--- a/nageru/queue_length_policy.h
+++ b/nageru/queue_length_policy.h
@@ -54,6 +54,7 @@ private:
 	std::deque<std::multiset<double>::iterator> history;
 
 	std::chrono::steady_clock::time_point expected_timestamp = std::chrono::steady_clock::time_point::min();
+	int64_t last_duration = 0;
 
 	// Metrics. There are no direct summaries for jitter, since we already have latency summaries.
 	std::atomic<int64_t> metric_input_underestimated_jitter_frames{0};