Add Extractor#release() implementation.

SubtitleExtractor.release() releases the underlying SubtitleDecoder.
This change introduces the STATE_RELEASED state. The extractor
handles the new state in the read() and seek() methods.

PiperOrigin-RevId: 391046478

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/subtitle/SubtitleExtractor.java

@@ -52,7 +52,8 @@ public class SubtitleExtractor implements Extractor {
         STATE_READING,
         STATE_DECODING,
         STATE_WRITING,
-        STATE_FINISHED
+        STATE_FINISHED,
+        STATE_RELEASED
       })
   @Retention(RetentionPolicy.SOURCE)
   private @interface State {}
@@ -69,6 +70,8 @@ public class SubtitleExtractor implements Extractor {
   private static final int STATE_WRITING = 4;
   /** The extractor has finished writing. */
   private static final int STATE_FINISHED = 5;
+  /** The extractor has bean released */
+  private static final int STATE_RELEASED = 6;
 
   private static final int DEFAULT_BUFFER_SIZE = 1024;
 
@@ -82,6 +85,11 @@ public class SubtitleExtractor implements Extractor {
   private int bytesRead;
   @State private int state;
 
+  /**
+   * @param subtitleDecoder The decoder used for decoding the subtitle data. The extractor will
+   *     release the decoder in {@link SubtitleExtractor#release()}.
+   * @param format Format that describes subtitle data.
+   */
   public SubtitleExtractor(SubtitleDecoder subtitleDecoder, Format format) {
     this.subtitleDecoder = subtitleDecoder;
     cueEncoder = new CueEncoder();
@@ -128,18 +136,25 @@ public class SubtitleExtractor implements Extractor {
       case STATE_FINISHED:
         return Extractor.RESULT_END_OF_INPUT;
       case STATE_CREATED:
+      case STATE_RELEASED:
       default:
         throw new IllegalStateException();
     }
   }
 
   @Override
-  public void seek(long position, long timeUs) {}
+  public void seek(long position, long timeUs) {
+    checkState(state != STATE_CREATED && state != STATE_RELEASED);
+  }
 
+  /** Releases the extractor's resources, including the {@link SubtitleDecoder}. */
   @Override
   public void release() {
-    // TODO: Proper implementation of this method is missing. Implement release() according to the
-    // Extractor interface documentation.
+    if (state == STATE_RELEASED) {
+      return;
+    }
+    subtitleDecoder.release();
+    state = STATE_RELEASED;
   }
 
   private void prepareMemory(ExtractorInput input) {

library/extractor/src/test/java/com/google/android/exoplayer2/extractor/subtitle/SubtitleExtractorTest.java

@@ -91,11 +91,56 @@ public class SubtitleExtractorTest {
   }
 
   @Test
-  public void read_notInitialized_fails() {
+  public void read_withoutInit_fails() {
     FakeExtractorInput input = new FakeExtractorInput.Builder().setData(new byte[0]).build();
     SubtitleExtractor extractor =
         new SubtitleExtractor(new WebvttDecoder(), new Format.Builder().build());
 
     assertThrows(IllegalStateException.class, () -> extractor.read(input, null));
   }
+
+  @Test
+  public void read_afterRelease_fails() {
+    FakeExtractorInput input = new FakeExtractorInput.Builder().setData(new byte[0]).build();
+    SubtitleExtractor extractor =
+        new SubtitleExtractor(new WebvttDecoder(), new Format.Builder().build());
+    FakeExtractorOutput output = new FakeExtractorOutput();
+
+    extractor.init(output);
+    extractor.release();
+
+    assertThrows(IllegalStateException.class, () -> extractor.read(input, null));
+  }
+
+  @Test
+  public void seek_withoutInit_fails() {
+    SubtitleExtractor extractor =
+        new SubtitleExtractor(new WebvttDecoder(), new Format.Builder().build());
+
+    assertThrows(IllegalStateException.class, () -> extractor.seek(0, 0));
+  }
+
+  @Test
+  public void seek_afterRelease_fails() {
+    SubtitleExtractor extractor =
+        new SubtitleExtractor(new WebvttDecoder(), new Format.Builder().build());
+    FakeExtractorOutput output = new FakeExtractorOutput();
+
+    extractor.init(output);
+    extractor.release();
+
+    assertThrows(IllegalStateException.class, () -> extractor.seek(0, 0));
+  }
+
+  @Test
+  public void released_calledTwice() {
+    SubtitleExtractor extractor =
+        new SubtitleExtractor(new WebvttDecoder(), new Format.Builder().build());
+    FakeExtractorOutput output = new FakeExtractorOutput();
+
+    extractor.init(output);
+    extractor.release();
+    extractor.release();
+    // Calling realease() twice does not throw an exception.
+  }
 }