From 5b106015de66665a2284db4a3923e2afb04d63c2 Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Sat, 22 Aug 2026 17:04:25 +1000
Subject: [PATCH] [client] audio: ignore jitter after underruns

Do not learn late delivery from packets that already caused an
underrun and media-clock rebase. Preserve learned jitter only across
continuous playback.
---
 client/src/audio.c          |  7 ++++---
 client/tests/CMakeLists.txt |  1 +
 client/tests/audio_test.c   | 31 +++++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/client/src/audio.c b/client/src/audio.c
index aae5add1..17c7e36e 100644
--- a/client/src/audio.c
+++ b/client/src/audio.c
@@ -924,7 +924,7 @@ static int64_t playbackMapMediaTime(PlaybackSourceData * sourceData,
   }
 
   const int64_t delta = time - sourceData->mediaTime;
-  if ((!clock || !clock->discontinuity) &&
+  if (!*discontinuity && (!clock || !clock->discontinuity) &&
       sourceData->mediaClockFromSource == fromSource &&
       sourceData->mediaPositionValid &&
       sourceData->mediaPosition == position && delta >= 0 &&
@@ -937,8 +937,9 @@ static int64_t playbackMapMediaTime(PlaybackSourceData * sourceData,
       (now - sourceData->lastArrivalTime) * 1.0e-9;
     const double lateness = max(arrivalDelta - mediaDelta, 0.0);
 
-    /* Learn harmful late delivery before a buffer underrun rebases the media
-     * clock. Early catch-up packets do not require additional reserve. */
+    /* Learn harmful late delivery only while playback remains continuous.
+     * An underrun rebases the media clock and must not become future
+     * latency. Early catch-up packets do not require additional reserve. */
     sourceData->arrivalJitterSec =
       min(PLAYBACK_MAX_JITTER_SEC,
           max(lateness, sourceData->arrivalJitterSec *
diff --git a/client/tests/CMakeLists.txt b/client/tests/CMakeLists.txt
index a9198e83..521c667b 100644
--- a/client/tests/CMakeLists.txt
+++ b/client/tests/CMakeLists.txt
@@ -819,6 +819,7 @@ if(ENABLE_AUDIO)
     convert
     provider
     playback-retry
+    jitter
     consent
     quiesce
   )
diff --git a/client/tests/audio_test.c b/client/tests/audio_test.c
index 5bb1a8bb..481743b4 100644
--- a/client/tests/audio_test.c
+++ b/client/tests/audio_test.c
@@ -624,6 +624,36 @@ static void testPlaybackRetry(void)
   stopAudio();
 }
 
+static void testPlaybackJitter(void)
+{
+  PlaybackSourceData source = { 0 };
+  playbackPrepareMediaClock(&source, NULL);
+
+  bool discontinuity = false;
+  playbackMapMediaTime(&source, NULL, 480, 48000, 0,
+      &discontinuity);
+  source.inputPosition   = 480;
+  source.lastArrivalTime = 0;
+
+  discontinuity = true;
+  playbackMapMediaTime(&source, NULL, 480, 48000,
+      INT64_C(110000000), &discontinuity);
+  CHECK(discontinuity);
+  CHECK(source.arrivalJitterSec == 0.0);
+
+  memset(&source, 0, sizeof(source));
+  playbackPrepareMediaClock(&source, NULL);
+  discontinuity = false;
+  playbackMapMediaTime(&source, NULL, 480, 48000, 0,
+      &discontinuity);
+  source.inputPosition   = 480;
+  source.lastArrivalTime = 0;
+  playbackMapMediaTime(&source, NULL, 480, 48000,
+      INT64_C(20000000), &discontinuity);
+  CHECK(source.arrivalJitterSec > 0.009);
+  CHECK(source.arrivalJitterSec < 0.011);
+}
+
 static void testConsent(void)
 {
   reset();
@@ -750,6 +780,7 @@ static const struct Test tests[] =
   { "convert"       , testConvert       },
   { "provider"      , testProvider      },
   { "playback-retry", testPlaybackRetry },
+  { "jitter"        , testPlaybackJitter },
   { "consent"       , testConsent       },
   { "quiesce"       , testQuiesce       },
 };