Decode on a single background thread; add intro skip key

PlaybackEngine now runs one daemon decode thread that routes packets into
bounded queues, while the video/audio presenter threads only consume and
pace. This removes the demuxer contention that caused stutter, bursts, and
the speed-up/catch-up behavior.

Press S (or media next) during playback to skip the current playlist and
advance the menu's intro chain quickly.

core/src/main/java/dev/quoije/umd/player/PlaybackEngine.java

@@ -9,7 +9,9 @@ import dev.quoije.umd.mps.AudioFramer;
 import dev.quoije.umd.mps.MpsDemuxer;
 
 import java.io.IOException;
-import java.util.ArrayDeque;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Decodes an MPS stream into timestamped video frames and PCM audio.
@@ -47,9 +49,12 @@ public final class PlaybackEngine implements AutoCloseable {
     private final AnnexBSplitter videoSplitter = new AnnexBSplitter();
     private final AudioFramer audioFramer = new AudioFramer();
 
+    private static final int VIDEO_QUEUE_CAPACITY = 16;
+    private static final int AUDIO_QUEUE_CAPACITY = 64;
+
     private Atrac3pDecoder audioDecoder;
-    private final ArrayDeque<VideoFrame> videoQueue = new ArrayDeque<>();
+    private final BlockingQueue<VideoFrame> videoQueue = new LinkedBlockingQueue<>(VIDEO_QUEUE_CAPACITY);
-    private final ArrayDeque<AudioChunk> audioQueue = new ArrayDeque<>();
+    private final BlockingQueue<AudioChunk> audioQueue = new LinkedBlockingQueue<>(AUDIO_QUEUE_CAPACITY);
 
     private long pendingVideoPts = -1;
     private long nextVideoPts = 0;
@@ -59,71 +64,98 @@ public final class PlaybackEngine implements AutoCloseable {
     private boolean audioPtsSet = false;
     private long audioFramesEmitted = 0;
 
-    private boolean eof = false;
+    private volatile boolean eof = false;
+    private volatile IOException failure = null;
+    private final Thread decodeThread;
 
     private PlaybackEngine(UmdIsoReader iso, String streamName, int audioSubstream) throws IOException {
         this.demuxer = MpsDemuxer.open(iso, streamName);
         this.audioSubstream = audioSubstream;
+        this.decodeThread = new Thread(this::decodeLoop, "umd-decode-" + streamName);
+        this.decodeThread.setDaemon(true);
     }
 
-    /** Opens the given playlist stream for playback, using the given audio substream (0 or 1). */
+    /** Opens the given playlist stream and starts decoding in the background. */
     public static PlaybackEngine open(UmdIsoReader iso, String streamName, int audioSubstream) throws IOException {
-        return new PlaybackEngine(iso, streamName, audioSubstream);
+        PlaybackEngine engine = new PlaybackEngine(iso, streamName, audioSubstream);
+        engine.decodeThread.start();
+        return engine;
     }
 
-    /**
+    /** The single decode thread: routes every packet and fills both queues. */
-     * Decodes until the next video frame is available, or end of stream.
+    private void decodeLoop() {
-     * Returns {@code null} at end of stream.
+        try {
-     */
+            while (true) {
-    public synchronized VideoFrame nextVideoFrame() throws IOException {
+                MpsDemuxer.Packet packet = demuxer.nextPacket();
-        int budget = 1000;
+                if (packet == null) {
-        while (videoQueue.isEmpty() && budget-- > 0) {
+                    finish();
-            if (!routeOne()) {
+                    break;
-                break;
+                }
+                if (packet.isVideo()) {
+                    handleVideo(packet);
+                } else if (packet.isAudio() && packet.channel() == audioSubstream) {
+                    handleAudio(packet);
+                }
+            }
+        } catch (InterruptedException e) {
+            // Closed; stop decoding.
+        } catch (IOException e) {
+            failure = e;
+        } finally {
+            eof = true;
+        }
+    }
+
+    /** Waits for the next video frame, or returns {@code null} at end of stream. */
+    public VideoFrame nextVideoFrame() throws IOException {
+        while (true) {
+            VideoFrame frame;
+            try {
+                frame = videoQueue.poll(50, TimeUnit.MILLISECONDS);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                return null;
+            }
+            if (frame != null) {
+                return frame;
+            }
+            if (eof && videoQueue.isEmpty()) {
+                if (failure != null) {
+                    throw failure;
+                }
+                return null;
             }
         }
-        return videoQueue.poll();
     }
 
-    /**
+    /** Waits for the next audio chunk, or returns {@code null} at end of stream. */
-     * Decodes until the next audio chunk is available, or end of stream.
+    public AudioChunk nextAudioChunk() throws IOException {
-     * Returns {@code null} at end of stream.
+        while (true) {
-     */
+            AudioChunk chunk;
-    public synchronized AudioChunk nextAudioChunk() throws IOException {
+            try {
-        int budget = 1000;
+                chunk = audioQueue.poll(50, TimeUnit.MILLISECONDS);
-        while (audioQueue.isEmpty() && budget-- > 0) {
+            } catch (InterruptedException e) {
-            if (!routeOne()) {
+                Thread.currentThread().interrupt();
-                break;
+                return null;
+            }
+            if (chunk != null) {
+                return chunk;
+            }
+            if (eof && audioQueue.isEmpty()) {
+                if (failure != null) {
+                    throw failure;
+                }
+                return null;
             }
         }
-        return audioQueue.poll();
     }
 
-    /** True once the stream has been fully decoded. */
+    /** True once the stream has been fully decoded and drained. */
-    public synchronized boolean isEof() {
+    public boolean isEof() {
         return eof && videoQueue.isEmpty() && audioQueue.isEmpty();
     }
 
-    /** Reads and routes one packet. Returns false at end of stream. */
+    private void handleVideo(MpsDemuxer.Packet packet) throws InterruptedException {
-    private boolean routeOne() throws IOException {
-        if (eof) {
-            return false;
-        }
-        MpsDemuxer.Packet packet = demuxer.nextPacket();
-        if (packet == null) {
-            finish();
-            eof = true;
-            return false;
-        }
-        if (packet.isVideo()) {
-            handleVideo(packet);
-        } else if (packet.isAudio() && packet.channel() == audioSubstream) {
-            handleAudio(packet);
-        }
-        return true;
-    }
-
-    private void handleVideo(MpsDemuxer.Packet packet) {
         if (packet.pts() >= 0) {
             if (pendingVideoPts < 0) {
                 nextVideoPts = packet.pts();
@@ -137,7 +169,7 @@ public final class PlaybackEngine implements AutoCloseable {
             videoDecoder.feedAccessUnit(accessUnit);
             VideoDecoder.Frame frame;
             while ((frame = videoDecoder.receive()) != null) {
-                videoQueue.add(new VideoFrame(
+                videoQueue.put(new VideoFrame(
                         assignVideoPts(), frame.width(), frame.height(),
                         frame.pixelFormat(), frame.yPlane(), frame.yStride(),
                         frame.uPlane(), frame.uStride(), frame.vPlane(), frame.vStride()));
@@ -167,7 +199,7 @@ public final class PlaybackEngine implements AutoCloseable {
         return videoFrameDurationTicks;
     }
 
-    private void handleAudio(MpsDemuxer.Packet packet) {
+    private void handleAudio(MpsDemuxer.Packet packet) throws InterruptedException {
         if (packet.pts() >= 0) {
             if (!audioPtsSet) {
                 audioFirstPts = packet.pts();
@@ -191,12 +223,12 @@ public final class PlaybackEngine implements AutoCloseable {
             audioDecoder.feedFrame(frame);
             byte[] pcm;
             while ((pcm = audioDecoder.receive()) != null) {
-                audioQueue.add(new AudioChunk(pts, pcm));
+                audioQueue.put(new AudioChunk(pts, pcm));
             }
         }
     }
 
-    private void finish() {
+    private void finish() throws InterruptedException {
         byte[] tail = videoSplitter.drain();
         if (tail != null && tail.length > 0) {
             videoDecoder.feedAccessUnit(tail);
@@ -204,7 +236,7 @@ public final class PlaybackEngine implements AutoCloseable {
         videoDecoder.flush();
         VideoDecoder.Frame frame;
         while ((frame = videoDecoder.receive()) != null) {
-            videoQueue.add(new VideoFrame(
+            videoQueue.put(new VideoFrame(
                     assignVideoPts(), frame.width(), frame.height(),
                     frame.pixelFormat(), frame.yPlane(), frame.yStride(),
                     frame.uPlane(), frame.uStride(), frame.vPlane(), frame.vStride()));
@@ -214,7 +246,7 @@ public final class PlaybackEngine implements AutoCloseable {
             audioDecoder.flush();
             byte[] pcm;
             while ((pcm = audioDecoder.receive()) != null) {
-                audioQueue.add(new AudioChunk(
+                audioQueue.put(new AudioChunk(
                         audioFirstPts + audioFramesEmitted * AUDIO_FRAME_TICKS, pcm));
             }
         }
@@ -222,6 +254,12 @@ public final class PlaybackEngine implements AutoCloseable {
 
     @Override
     public void close() {
+        decodeThread.interrupt();
+        try {
+            decodeThread.join(1000);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
         videoDecoder.close();
         if (audioDecoder != null) {
             audioDecoder.close();

ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java

@@ -64,6 +64,7 @@ public final class PlayerApp extends Application {
     private final WritableImage[] videoImages = new WritableImage[2];
     private final int[][] argbBuffers = new int[2][];
     private int videoBufferIndex = 0;
+    private volatile boolean skipRequested = false;
 
     @Override
     public void start(Stage stage) {
@@ -114,6 +115,10 @@ public final class PlayerApp extends Application {
                 togglePause();
                 return;
             }
+            case S, TRACK_NEXT -> {
+                skipRequested = true;
+                return;
+            }
             default -> { }
         }
 
@@ -202,6 +207,10 @@ public final class PlayerApp extends Application {
 
                 PlaybackEngine.VideoFrame frame;
                 while ((frame = engine.nextVideoFrame()) != null) {
+                    if (skipRequested) {
+                        skipRequested = false;
+                        break;
+                    }
                     int index = videoBufferIndex++ & 1;
                     int[] argb = argbBuffers[index];
                     int pixelCount = frame.width() * frame.height();