Fix 'legacy' CEA-608 and CEA-708 to use the Decoder impls

We deliberately left `Cea608Decoder` and `Cea708Decoder` intact when
creating the respective `SubtitleParser` implementations (in
27caeb8
and
94e45eb
respectively).

However we didn't correctly change the behaviour of
`SubtitleDecoderFactory.DEFAULT` in order to use these 'legacy'
implementations. We firstly left the `Cea608Decoder` instantiation
**after** the `DefaultSubtitleParserFactory.supportsFormat()` check,
meaning that code would never be reached (since `supportsFormat` now
returns true for CEA-608). Then in the second change (which was supposed
to only be about CEA-708) we removed all instantiations of **both**
`Cea608Decoder` and `Cea708Decoder`. This change puts the decoder
instantiations back and moves them above the
`DefaultSubtitleParserFactory.supportsFormat` check, meaning they will
be used in preference to `DelegatingSubtitleDecoder`.

This resolves the immediately-disappearing subtitles tracked by
Issue: #904.
PiperOrigin-RevId: 592217937

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/text/SubtitleDecoderFactory.java

@@ -17,10 +17,16 @@
 
 import androidx.annotation.Nullable;
 import androidx.media3.common.Format;
+import androidx.media3.common.MimeTypes;
 import androidx.media3.common.util.UnstableApi;
 import androidx.media3.extractor.text.DefaultSubtitleParserFactory;
 import androidx.media3.extractor.text.SubtitleDecoder;
 import androidx.media3.extractor.text.SubtitleParser;
+import androidx.media3.extractor.text.cea.Cea608Decoder;
+import androidx.media3.extractor.text.cea.Cea608Parser;
+import androidx.media3.extractor.text.cea.Cea708Decoder;
+import androidx.media3.extractor.text.cea.Cea708Parser;
+import java.util.Objects;
 
 /** A factory for {@link SubtitleDecoder} instances. */
 @UnstableApi
@@ -47,7 +53,12 @@ public interface SubtitleDecoderFactory {
   /**
    * Default {@link SubtitleDecoderFactory} implementation.
    *
-   * <p>Only supports formats supported by {@link DefaultSubtitleParserFactory}.
+   * <p>Supports formats supported by {@link DefaultSubtitleParserFactory} as well as the following:
+   *
+   * <ul>
+   *   <li>Cea608 ({@link Cea608Decoder})
+   *   <li>Cea708 ({@link Cea708Decoder})
+   * </ul>
    */
   SubtitleDecoderFactory DEFAULT =
       new SubtitleDecoderFactory() {
@@ -56,17 +67,37 @@ public interface SubtitleDecoderFactory {
 
         @Override
         public boolean supportsFormat(Format format) {
-          return delegate.supportsFormat(format);
+          @Nullable String mimeType = format.sampleMimeType;
+          return delegate.supportsFormat(format)
+              || Objects.equals(mimeType, MimeTypes.APPLICATION_CEA608)
+              || Objects.equals(mimeType, MimeTypes.APPLICATION_MP4CEA608)
+              || Objects.equals(mimeType, MimeTypes.APPLICATION_CEA708);
         }
 
         @Override
         public SubtitleDecoder createDecoder(Format format) {
+          @Nullable String mimeType = format.sampleMimeType;
+          if (mimeType != null) {
+            switch (mimeType) {
+              case MimeTypes.APPLICATION_CEA608:
+              case MimeTypes.APPLICATION_MP4CEA608:
+                return new Cea608Decoder(
+                    new Cea608Parser(
+                        mimeType,
+                        format.accessibilityChannel,
+                        Cea608Parser.MIN_DATA_CHANNEL_TIMEOUT_MS));
+              case MimeTypes.APPLICATION_CEA708:
+                return new Cea708Decoder(
+                    new Cea708Parser(format.accessibilityChannel, format.initializationData));
+              default:
+                break;
+            }
+          }
           if (delegate.supportsFormat(format)) {
             SubtitleParser subtitleParser = delegate.create(format);
             return new DelegatingSubtitleDecoder(
                 subtitleParser.getClass().getSimpleName() + "Decoder", subtitleParser);
           }
-          @Nullable String mimeType = format.sampleMimeType;
           throw new IllegalArgumentException(
               "Attempted to create decoder for unsupported MIME type: " + mimeType);
         }