Add playback engine with A/V timestamping

- AnnexBSplitter incrementally splits the Annex-B stream into access
  units, holding partial slices across packet feeds.
- VideoDecoder exposes feedAccessUnit and the decoded frame rate.
- PlaybackEngine demuxes and decodes in lockstep, tagging video frames
  and audio chunks with 90 kHz PTS (audio from PES headers, video from
  PES anchors interpolated by decoder frame rate).
- CLI 'play' command runs the engine headlessly and reports A/V drift.
- Validated against Batman Begins: 95 frames in 4.0s, max drift -78.6 ms
  (video trails audio at stream start), avg frame duration 3833.6 ticks.
- Tests for AnnexBSplitter.

cli/src/main/java/dev/quoije/umd/cli/Main.java

@@ -7,6 +7,7 @@ import dev.quoije.umd.media.Atrac3pDecoder;
 import dev.quoije.umd.media.VideoDecoder;
 import dev.quoije.umd.mps.AudioFramer;
 import dev.quoije.umd.mps.MpsDemuxer;
+import dev.quoije.umd.player.PlaybackEngine;
 import dev.quoije.umd.playlist.Playlist;
 import dev.quoije.umd.sfo.Sfo;
 
@@ -19,7 +20,7 @@ import java.util.Map;
 /** Command-line front-end for the UMD player library. */
 public final class Main {
 
-    private static final String USAGE = "usage: umdplayer dump <image.iso>\n       umdplayer mps <image.iso> <streamName>\n       umdplayer decode <image.iso> <streamName>\n       umdplayer audio <image.iso> <streamName> [count]\n       umdplayer adecode <image.iso> <streamName> [maxPackets]";
+    private static final String USAGE = "usage: umdplayer dump <image.iso>\n       umdplayer mps <image.iso> <streamName>\n       umdplayer decode <image.iso> <streamName>\n       umdplayer audio <image.iso> <streamName> [count]\n       umdplayer adecode <image.iso> <streamName> [maxPackets]\n       umdplayer play <image.iso> <streamName> [seconds]";
 
     private Main() {
     }
@@ -38,6 +39,7 @@ public final class Main {
                 case "decode" -> decode(requireArg(args, 1), requireArg(args, 2));
                 case "audio" -> audio(requireArg(args, 1), requireArg(args, 2), args.length > 3 ? Integer.parseInt(args[3]) : 8);
                 case "adecode" -> adecode(requireArg(args, 1), requireArg(args, 2), args.length > 3 ? Integer.parseInt(args[3]) : 500);
+                case "play" -> play(requireArg(args, 1), requireArg(args, 2), args.length > 3 ? Double.parseDouble(args[3]) : 5.0);
                 case "help", "--help", "-h" -> {
                     System.out.println(USAGE);
                     yield 0;
@@ -333,6 +335,55 @@ public final class Main {
         return 0;
     }
 
+    private static int play(String imagePath, String streamName, double seconds) throws IOException {
+        long targetPts = (long) (seconds * PlaybackEngine.MPEG_TIMESTAMP);
+        try (UmdIsoReader iso = new UmdIsoReader(Path.of(imagePath));
+             PlaybackEngine engine = PlaybackEngine.open(iso, streamName, 0)) {
+
+            int frames = 0;
+            long firstPts = -1;
+            long lastPts = -1;
+            long audioClock = -1;
+            long maxDrift = 0;
+
+            PlaybackEngine.VideoFrame frame;
+            while ((frame = engine.nextVideoFrame()) != null) {
+                if (firstPts < 0) {
+                    firstPts = frame.pts();
+                }
+                lastPts = frame.pts();
+                frames++;
+
+                // Advance the audio clock to at least this frame's timestamp.
+                while (audioClock < frame.pts()) {
+                    PlaybackEngine.AudioChunk chunk = engine.nextAudioChunk();
+                    if (chunk == null) {
+                        break;
+                    }
+                    audioClock = chunk.pts() + PlaybackEngine.AUDIO_FRAME_TICKS;
+                }
+
+                long drift = frame.pts() - audioClock;
+                if (Math.abs(drift) > Math.abs(maxDrift)) {
+                    maxDrift = drift;
+                }
+
+                if (frame.pts() >= targetPts) {
+                    break;
+                }
+            }
+
+            double spanSeconds = (lastPts - firstPts) / (double) PlaybackEngine.MPEG_TIMESTAMP;
+            double frameDuration = frames > 1 ? (lastPts - firstPts) / (double) (frames - 1) : 0;
+            System.out.printf("video: %d frames, pts %d..%d (%.2fs), avg frame duration %.2f ticks%n",
+                    frames, firstPts, lastPts, spanSeconds, frameDuration);
+            System.out.printf("audio clock: %d (%.2fs), max |video-audio| drift: %d ticks (%.1f ms)%n",
+                    audioClock, audioClock / (double) PlaybackEngine.MPEG_TIMESTAMP,
+                    maxDrift, maxDrift * 1000.0 / PlaybackEngine.MPEG_TIMESTAMP);
+        }
+        return 0;
+    }
+
     private static String hexPrefix(byte[] data, int max) {
         StringBuilder sb = new StringBuilder();
         for (int i = 0; i < Math.min(data.length, max); i++) {