[client] audio: fix underrun clock recovery

Recover stable local playback in the device clock domain and restart
rate control from the measured feed-forward clock ratio.

Ignore catch-up packet sizing until the normal source cadence returns.

client/src/audio.c

@@ -173,7 +173,9 @@ typedef struct
   double       sourcePhaseBaselineSec;
   double       sourcePhaseReserveSec;
   double       sourcePacketDurationSec;
+  unsigned int sourcePacketPacedCount;
   bool         sourcePhaseBaselineValid;
+  bool         sourcePacketRecovering;
   bool         mediaClockValid;
   bool         mediaPositionValid;
   bool         mediaClockFromSource;
@@ -1438,7 +1440,9 @@ static bool playbackStart(const LG_AudioFormat * format,
   audio.playback.sourceData.sourcePhaseBaselineSec   = 0.0;
   audio.playback.sourceData.sourcePhaseReserveSec    = 0.0;
   audio.playback.sourceData.sourcePacketDurationSec  = 0.0;
+  audio.playback.sourceData.sourcePacketPacedCount   = 0;
   audio.playback.sourceData.sourcePhaseBaselineValid = false;
+  audio.playback.sourceData.sourcePacketRecovering   = false;
   audio.playback.sourceData.deviceClock.valid        = false;
   audio.playback.sourceData.outputClock.valid        = false;
   playbackPrepareMediaClock(&audio.playback.sourceData, sourceClock);
@@ -2130,6 +2134,26 @@ static int playbackSlewBuffer(
   return advanced;
 }
 
+static bool playbackUseLowWaterRecovery(bool providerRateControl,
+    bool bufferUnderrun, const PlaybackSourceData * sourceData)
+{
+  return providerRateControl ||
+    (bufferUnderrun && (!sourceData->deviceClock.valid ||
+      !sourceData->deviceClockStable));
+}
+
+static void playbackResetRateControl(PlaybackSourceData * sourceData,
+    bool providerRateControl)
+{
+  sourceData->offsetError         = 0.0;
+  sourceData->offsetErrorIntegral = 0.0;
+  sourceData->ratioIntegral       = 0.0;
+  sourceData->lastRatio           = providerRateControl ?
+    1.0 : sourceData->lastClockRatio;
+  if (providerRateControl)
+    sourceData->nextFeedbackTime = 0;
+}
+
 static PlaybackDataResult playbackData(const void * data, size_t frameCount,
     const LG_AudioClock * sourceClock, int64_t arrivalTime)
 {
@@ -2201,6 +2225,7 @@ static PlaybackDataResult playbackData(const void * data, size_t frameCount,
     ringbuffer_getCount(audio.playback.buffer) < 0;
   bool discontinuity                =
     bufferUnderrun || (sourceClock && sourceClock->discontinuity);
+  const int64_t previousArrivalTime = sourceData->lastArrivalTime;
   const int64_t packetTime          =
     playbackMapMediaTime(sourceData, sourceClock, frames,
         audio.playback.sampleRate, arrivalTime, &discontinuity);
@@ -2251,9 +2276,46 @@ static PlaybackDataResult playbackData(const void * data, size_t frameCount,
     sourceData->sourceClock.phaseResidualSec;
   const double packetSec                =
     frames * nominalFrameSec;
+  const double decayedPacketDurationSec =
+    sourceData->sourcePacketDurationSec *
+      exp(-packetSec / PLAYBACK_PHASE_RESERVE_DECAY_SEC);
+  const bool cadenceReset               = discontinuity ||
+    state == STREAM_STATE_KEEP_ALIVE ||
+    state == STREAM_STATE_RESUMING;
+  if (cadenceReset && sourceData->sourcePacketDurationSec > 0.0)
+  {
+    sourceData->sourcePacketRecovering = true;
+    sourceData->sourcePacketPacedCount = 0;
+  }
+  else if (sourceData->sourcePacketRecovering)
+  {
+    if (packetSec <= decayedPacketDurationSec + nominalFrameSec)
+    {
+      sourceData->sourcePacketRecovering = false;
+      sourceData->sourcePacketPacedCount = 0;
+    }
+    else
+    {
+      const bool paced = previousArrivalTime != INT64_MIN &&
+        arrivalTime > previousArrivalTime &&
+        (arrivalTime - previousArrivalTime) * 2.0e-9 >= packetSec;
+      sourceData->sourcePacketPacedCount = paced ?
+        sourceData->sourcePacketPacedCount + 1 : 0;
+      if (sourceData->sourcePacketPacedCount >= 2)
+      {
+        sourceData->sourcePacketRecovering = false;
+        sourceData->sourcePacketPacedCount = 0;
+      }
+    }
+  }
+
+  /* Catch-up packets describe audio accumulated during a gap, not the future
+   * delivery cadence. Resume when the prior cadence returns or a larger
+   * cadence is confirmed by consecutive plausibly paced packets. */
   sourceData->sourcePacketDurationSec =
-    max(packetSec, sourceData->sourcePacketDurationSec *
-        exp(-packetSec / PLAYBACK_PHASE_RESERVE_DECAY_SEC));
+    !sourceData->sourcePacketRecovering ?
+      max(packetSec, decayedPacketDurationSec) :
+      decayedPacketDurationSec;
 
   if (!sourceData->sourcePhaseBaselineValid ||
       sourceData->sourceClock.updates == 1)
@@ -2396,7 +2458,8 @@ static PlaybackDataResult playbackData(const void * data, size_t frameCount,
 
   double devPosition = DBL_MIN;
   state = playbackGetState();
-  if ((providerRateControl || bufferUnderrun) &&
+  if (playbackUseLowWaterRecovery(providerRateControl,
+        bufferUnderrun, sourceData) &&
       (discontinuity ||
        state == STREAM_STATE_KEEP_ALIVE ||
        state == STREAM_STATE_RESUMING))
@@ -2409,14 +2472,7 @@ static PlaybackDataResult playbackData(const void * data, size_t frameCount,
     sourceData->outputPosition += actualSlew;
     curPosition += actualSlew;
 
-    sourceData->offsetError         = 0.0;
-    sourceData->offsetErrorIntegral = 0.0;
-    sourceData->ratioIntegral       = 0.0;
-    if (providerRateControl && bufferUnderrun)
-    {
-      sourceData->lastRatio        = 1.0;
-      sourceData->nextFeedbackTime = 0;
-    }
+    playbackResetRateControl(sourceData, providerRateControl);
     if (state == STREAM_STATE_KEEP_ALIVE ||
         state == STREAM_STATE_RESUMING)
       atomic_compare_exchange_strong_explicit(
@@ -2437,9 +2493,7 @@ static PlaybackDataResult playbackData(const void * data, size_t frameCount,
     sourceData->outputPosition += actualSlew;
     curPosition += actualSlew;
 
-    sourceData->offsetError         = 0.0;
-    sourceData->offsetErrorIntegral = 0.0;
-    sourceData->ratioIntegral       = 0.0;
+    playbackResetRateControl(sourceData, providerRateControl);
     if (state == STREAM_STATE_KEEP_ALIVE ||
         state == STREAM_STATE_RESUMING)
       atomic_compare_exchange_strong_explicit(

client/tests/CMakeLists.txt

@@ -820,6 +820,7 @@ if(ENABLE_AUDIO)
     provider
     playback-retry
     jitter
+    recovery
     consent
     quiesce
   )

client/tests/audio_test.c

@@ -654,6 +654,54 @@ static void testPlaybackJitter(void)
   CHECK(source.arrivalJitterSec < 0.011);
 }
 
+static void testPlaybackRecovery(void)
+{
+  reset();
+  startAudio();
+
+  const LG_AudioFormat format = makeFormat(LG_AUDIO_FMT_S16_LE);
+  CHECK(playbackStart(&format, NULL, false, false));
+  CHECK(audio.playback.rateControl == PLAYBACK_RATE_BACKEND);
+  playbackSetState(STREAM_STATE_RUN);
+
+  PlaybackSourceData * source = &audio.playback.sourceData;
+  const int64_t arrival       = nanotime();
+  playbackClockReset(&source->deviceClock,
+      arrival, 0.0, 1.0 / format.sampleRate);
+  source->deviceClockStable       = true;
+  source->outputPosition          = 0;
+  source->lastRatio               = 0.999;
+  source->lastClockRatio          = 1.0002;
+  source->sourcePacketDurationSec = 0.010;
+  playbackPublishDeviceTiming(16, arrival, 0, 0.0, 0);
+
+  CHECK(ringbuffer_consume(audio.playback.buffer, NULL, 16) == 16);
+  CHECK(ringbuffer_getCount(audio.playback.buffer) == -16);
+  uint8_t frames[1200 * 2 * 2] = { 0 };
+  CHECK(playbackData(frames, 1200, NULL, arrival) ==
+      PLAYBACK_DATA_PROCESSED);
+
+  CHECK(source->sourcePacketDurationSec < 0.010);
+  CHECK(source->sourcePacketDurationSec > 0.009);
+  CHECK(source->sourcePacketRecovering);
+  CHECK(source->outputPosition == 1770);
+  CHECK(ringbuffer_getCount(audio.playback.buffer) == 1754);
+  CHECK(fabs(atomic_load(&audio.playback.backendResampleRatio) -
+        source->lastClockRatio) < 0.000001);
+
+  CHECK(playbackData(frames, 1200, NULL, arrival + 1000) ==
+      PLAYBACK_DATA_PROCESSED);
+  CHECK(source->sourcePacketDurationSec < 0.010);
+  CHECK(source->sourcePacketRecovering);
+
+  CHECK(playbackData(frames, 480, NULL,
+        arrival + INT64_C(10000000)) == PLAYBACK_DATA_PROCESSED);
+  CHECK(!source->sourcePacketRecovering);
+  CHECK(fabs(source->sourcePacketDurationSec - 0.010) < 0.000001);
+
+  stopAudio();
+}
+
 static void testConsent(void)
 {
   reset();
@@ -781,6 +829,7 @@ static const struct Test tests[] =
   { "provider"      , testProvider      },
   { "playback-retry", testPlaybackRetry },
   { "jitter"        , testPlaybackJitter },
+  { "recovery"      , testPlaybackRecovery },
   { "consent"       , testConsent       },
   { "quiesce"       , testQuiesce       },
 };