Play ATRAC3+ audio through the system audio line

The audio thread writes decoded PCM to a SourceDataLine and acts as the
master A/V clock; video frames are now paced against that shared clock so
audio and video stay in sync.

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

@@ -29,6 +29,10 @@ import javafx.scene.layout.StackPane;
 import javafx.scene.paint.Color;
 import javafx.stage.Stage;
 
+import javax.sound.sampled.AudioFormat;
+import javax.sound.sampled.AudioSystem;
+import javax.sound.sampled.SourceDataLine;
+
 import java.io.IOException;
 import java.nio.file.Path;
 
@@ -45,6 +49,10 @@ public final class PlayerApp extends Application {
     private volatile MoviePlayer moviePlayer;
     private Stage stage;
 
+    /** Master A/V clock anchor, set by the audio thread. */
+    private volatile long clockStartPts = -1;
+    private volatile long clockStartNanos = -1;
+
     @Override
     public void start(Stage stage) {
         // Gradle's --args splits on whitespace; rejoin so paths with spaces work.
@@ -164,8 +172,10 @@ public final class PlayerApp extends Application {
             try (UmdIsoReader iso = new UmdIsoReader(Path.of(isoPath));
                  PlaybackEngine engine = PlaybackEngine.open(iso, streamName, 0)) {
 
-                long basePts = -1;
+                startAudio(engine);
-                long baseNanos = -1;
+                awaitClock();
+                long basePts = clockStartPts;
+                long baseNanos = clockStartNanos;
 
                 PlaybackEngine.VideoFrame frame;
                 while ((frame = engine.nextVideoFrame()) != null) {
@@ -175,17 +185,8 @@ public final class PlayerApp extends Application {
                             frame.vPlane(), frame.vStride());
                     blitVideo(argb, frame.width(), frame.height());
 
-                    if (basePts < 0) {
-                        basePts = frame.pts();
-                        baseNanos = System.nanoTime();
-                    }
                     long targetNanos = baseNanos + (frame.pts() - basePts) * 1_000_000_000L / PlaybackEngine.MPEG_TIMESTAMP;
-                    long sleepNanos = targetNanos - System.nanoTime();
+                    sleepUntil(targetNanos);
-                    if (sleepNanos > 0) {
-                        long millis = sleepNanos / 1_000_000;
-                        int nanos = (int) (sleepNanos % 1_000_000);
-                        Thread.sleep(millis, nanos);
-                    }
                 }
 
                 MoviePlayer mp = moviePlayer;
@@ -200,6 +201,67 @@ public final class PlayerApp extends Application {
         player.start();
     }
 
+    /** Plays decoded PCM through the system audio line, acting as the master A/V clock. */
+    private void startAudio(PlaybackEngine engine) {
+        Thread audio = new Thread(() -> {
+            SourceDataLine line = null;
+            try {
+                line = openLine();
+                PlaybackEngine.AudioChunk chunk;
+                while ((chunk = engine.nextAudioChunk()) != null) {
+                    if (clockStartPts < 0) {
+                        clockStartPts = chunk.pts();
+                        clockStartNanos = System.nanoTime();
+                    }
+                    long targetNanos = clockStartNanos
+                            + (chunk.pts() - clockStartPts) * 1_000_000_000L / PlaybackEngine.MPEG_TIMESTAMP;
+                    sleepUntil(targetNanos);
+                    line.write(chunk.pcm(), 0, chunk.pcm().length);
+                }
+                line.drain();
+            } catch (Exception e) {
+                e.printStackTrace();
+            } finally {
+                if (line != null) {
+                    line.close();
+                }
+                if (clockStartPts < 0) {
+                    clockStartPts = 0;
+                    clockStartNanos = System.nanoTime();
+                }
+            }
+        }, "audio-player");
+        audio.setDaemon(true);
+        audio.start();
+    }
+
+    private static SourceDataLine openLine() throws Exception {
+        AudioFormat format = new AudioFormat(PlaybackEngine.AUDIO_SAMPLE_RATE, 16, 2, true, false);
+        SourceDataLine line = AudioSystem.getSourceDataLine(format);
+        line.open(format, PlaybackEngine.AUDIO_SAMPLE_RATE * 4);
+        line.start();
+        return line;
+    }
+
+    /** Waits until the audio thread anchors the master clock, or falls back. */
+    private void awaitClock() throws InterruptedException {
+        long deadline = System.nanoTime() + 5_000_000_000L;
+        while (clockStartPts < 0 && System.nanoTime() < deadline) {
+            Thread.sleep(2);
+        }
+        if (clockStartPts < 0) {
+            clockStartPts = 0;
+            clockStartNanos = System.nanoTime();
+        }
+    }
+
+    private static void sleepUntil(long targetNanos) throws InterruptedException {
+        long sleepNanos = targetNanos - System.nanoTime();
+        if (sleepNanos > 0) {
+            Thread.sleep(sleepNanos / 1_000_000, (int) (sleepNanos % 1_000_000));
+        }
+    }
+
     private void blitVideo(int[] argb, int width, int height) {
         WritableImage image = new WritableImage(width, height);
         image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getIntArgbInstance(), argb, 0, width);