diff --git a/core/src/main/java/dev/quoije/umd/player/PlaybackEngine.java b/core/src/main/java/dev/quoije/umd/player/PlaybackEngine.java
index 35618c2..a0abcca 100644
--- a/core/src/main/java/dev/quoije/umd/player/PlaybackEngine.java
+++ b/core/src/main/java/dev/quoije/umd/player/PlaybackEngine.java
@@ -75,7 +75,7 @@ public final class PlaybackEngine implements AutoCloseable {
      * Decodes until the next video frame is available, or end of stream.
      * Returns {@code null} at end of stream.
      */
-    public VideoFrame nextVideoFrame() throws IOException {
+    public synchronized VideoFrame nextVideoFrame() throws IOException {
         int budget = 1000;
         while (videoQueue.isEmpty() && budget-- > 0) {
             if (!routeOne()) {
@@ -89,7 +89,7 @@ public final class PlaybackEngine implements AutoCloseable {
      * Decodes until the next audio chunk is available, or end of stream.
      * Returns {@code null} at end of stream.
      */
-    public AudioChunk nextAudioChunk() throws IOException {
+    public synchronized AudioChunk nextAudioChunk() throws IOException {
         int budget = 1000;
         while (audioQueue.isEmpty() && budget-- > 0) {
             if (!routeOne()) {
@@ -100,7 +100,7 @@ public final class PlaybackEngine implements AutoCloseable {
     }
 
     /** True once the stream has been fully decoded. */
-    public boolean isEof() {
+    public synchronized boolean isEof() {
         return eof && videoQueue.isEmpty() && audioQueue.isEmpty();
     }
 
diff --git a/ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java b/ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java
index 90f8055..fd57c1d 100644
--- a/ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java
+++ b/ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java
@@ -195,7 +195,7 @@ public final class PlayerApp extends Application {
             try (UmdIsoReader iso = new UmdIsoReader(Path.of(isoPath));
                  PlaybackEngine engine = PlaybackEngine.open(iso, streamName, 0)) {
 
-                startAudio(engine);
+                Thread audio = startAudio(engine);
                 awaitClock();
                 long basePts = clockStartPts;
                 long baseNanos = clockStartNanos;
@@ -219,6 +219,10 @@ public final class PlayerApp extends Application {
                     sleepUntil(targetNanos);
                 }
 
+                // Wait for the audio thread to finish draining before the
+                // engine (and its decoders) is closed by this try block.
+                audio.join(2000);
+
                 MoviePlayer mp = moviePlayer;
                 if (mp != null) {
                     mp.onPlayListEnd(playListNumber);
@@ -232,7 +236,7 @@ public final class PlayerApp extends Application {
     }
 
     /** Plays decoded PCM through the system audio line, acting as the master A/V clock. */
-    private void startAudio(PlaybackEngine engine) {
+    private Thread startAudio(PlaybackEngine engine) {
         Thread audio = new Thread(() -> {
             SourceDataLine line = null;
             try {
@@ -264,6 +268,7 @@ public final class PlayerApp extends Application {
         }, "audio-player");
         audio.setDaemon(true);
         audio.start();
+        return audio;
     }
 
     private static SourceDataLine openLine() throws Exception {