Suppress underrun events when a format change is pending

Sources/CSFBAudioEngine/Player/AudioPlayer.h

@@ -207,8 +207,10 @@ class AudioPlayer final {
         isMuted = 1u << 2,
         /// The ring buffer needs to be drained during the next render cycle
         drainRequired = 1u << 3,
+        /// A ring buffer format change is pending
+        pendingFormatChange = 1u << 4,
         /// The event message queue had insufficient space to record a render event
-        renderEventDropped = 1u << 4,
+        renderEventDropped = 1u << 5,
     };
 
     // Enable bitmask operations for `Flags`

Sources/CSFBAudioEngine/Player/AudioPlayer.mm

@@ -1423,13 +1423,16 @@ Flags clearFlags(Flags flags, std::memory_order order = std::memory_order_acq_re
                 }();
 
                 if (okToReconfigure) {
-                    clearFlags(Flags::drainRequired);
-                    formatMismatch = false;
-
                     os_log_debug(log_, "Non-gapless join for %{public}@", decoderState->decoder_);
 
                     auto renderFormat = decoderState->converter_.outputFormat;
-                    if (NSError *error = nil; !configureProcessingGraphAndRingBufferForFormat(renderFormat, &error)) {
+                    NSError *error = nil;
+                    const auto reconfigured = configureProcessingGraphAndRingBufferForFormat(renderFormat, &error);
+
+                    clearFlags(Flags::drainRequired | Flags::pendingFormatChange);
+                    formatMismatch = false;
+
+                    if (!reconfigured) {
                         decoderState->error_ = error;
                         decoderState->setFlags(DecoderState::Flags::cancelRequested);
                         continue;
@@ -1452,6 +1455,7 @@ Flags clearFlags(Flags flags, std::memory_order order = std::memory_order_acq_re
                         }
                     }
                 } else {
+                    setFlags(Flags::pendingFormatChange);
                     decoderState = nullptr;
                 }
             }
@@ -1606,7 +1610,8 @@ Flags clearFlags(Flags flags, std::memory_order order = std::memory_order_acq_re
         isSilence = YES;
     }
 
-    if (framesRead != frameCount) {
+    // A short frame count without a pending format change is unexpected
+    if (framesRead != frameCount && bits::is_clear(flags, Flags::pendingFormatChange)) {
         if (!events_.enqueue(EventCommand::renderBufferUnderrun, timestamp.mHostTime, static_cast<uint32_t>(framesRead),
                              static_cast<uint32_t>(frameCount))) {
             setFlags(Flags::renderEventDropped);