Avoid selecting a forced text track that doesn't match the audio selection

Assuming there is no text language preference.

PiperOrigin-RevId: 244176667

RELEASENOTES.md

@@ -44,7 +44,7 @@
   * MP3: Fix ID3 frame unsychronization
     ([#5673](https://github.com/google/ExoPlayer/issues/5673)).
   * MP3: Fix playback of badly clipped files
-    ([#5772](https://github.com/google/ExoPlayer/issues/5772)).  
+    ([#5772](https://github.com/google/ExoPlayer/issues/5772)).
   * MPEG-TS: Enable HDMV DTS stream detection only if a flag is set. By default
     (i.e. if the flag is not set), the 0x82 elementary stream type is now
     treated as an SCTE subtitle track
@@ -55,6 +55,8 @@
   * Update `TrackSelection.Factory` interface to support creating all track
     selections together.
   * Allow to specify a selection reason for a `SelectionOverride`.
+  * When no text language preference matches, only select forced text tracks
+    whose language matches the selected audio language.
 * UI:
   * Update `DefaultTimeBar` based on duration of media and add parameter to set
     the minimum update interval to control the smoothness of the updates

library/core/src/main/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelector.java

@@ -2070,29 +2070,25 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           boolean isForced = (maskedSelectionFlags & C.SELECTION_FLAG_FORCED) != 0;
           int trackScore;
           int languageScore = getFormatLanguageScore(format, params.preferredTextLanguage);
-          if (languageScore > 0
+          boolean trackHasNoLanguage = formatHasNoLanguage(format);
-              || (params.selectUndeterminedTextLanguage && formatHasNoLanguage(format))) {
+          if (languageScore > 0 || (params.selectUndeterminedTextLanguage && trackHasNoLanguage)) {
             if (isDefault) {
-              trackScore = 17;
+              trackScore = 11;
             } else if (!isForced) {
               // Prefer non-forced to forced if a preferred text language has been specified. Where
               // both are provided the non-forced track will usually contain the forced subtitles as
               // a subset.
-              trackScore = 13;
+              trackScore = 7;
             } else {
-              trackScore = 9;
+              trackScore = 3;
             }
             trackScore += languageScore;
           } else if (isDefault) {
-            trackScore = 8;
+            trackScore = 2;
-          } else if (isForced) {
+          } else if (isForced
-            int preferredAudioLanguageScore =
+              && (getFormatLanguageScore(format, selectedAudioLanguage) > 0
-                getFormatLanguageScore(format, params.preferredAudioLanguage);
+                  || (trackHasNoLanguage && stringDefinesNoLanguage(selectedAudioLanguage)))) {
-            if (preferredAudioLanguageScore > 0) {
+            trackScore = 1;
-              trackScore = 4 + preferredAudioLanguageScore;
-            } else {
-              trackScore = 1 + getFormatLanguageScore(format, selectedAudioLanguage);
-            }
           } else {
             // Track should not be selected.
             continue;
@@ -2281,15 +2277,19 @@ public class DefaultTrackSelector extends MappingTrackSelector {
         && maskedSupport == RendererCapabilities.FORMAT_EXCEEDS_CAPABILITIES);
   }
 
-  /**
+  /** Equivalent to {@link #stringDefinesNoLanguage stringDefinesNoLanguage(format.language)}. */
-   * Returns whether a {@link Format} does not define a language.
-   *
-   * @param format The {@link Format}.
-   * @return Whether the {@link Format} does not define a language.
-   */
   protected static boolean formatHasNoLanguage(Format format) {
-    return TextUtils.isEmpty(format.language)
+    return stringDefinesNoLanguage(format.language);
-        || TextUtils.equals(format.language, C.LANGUAGE_UNDETERMINED);
+  }
+
+  /**
+   * Returns whether the given string does not define a language.
+   *
+   * @param language The string.
+   * @return Whether the given string does not define a language.
+   */
+  protected static boolean stringDefinesNoLanguage(@Nullable String language) {
+    return TextUtils.isEmpty(language) || TextUtils.equals(language, C.LANGUAGE_UNDETERMINED);
   }
 
   /**

library/core/src/test/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelectorTest.java

@@ -910,13 +910,8 @@ public final class DefaultTrackSelectorTest {
     result = trackSelector.selectTracks(textRendererCapabilities, trackGroups, periodId, TIMELINE);
     assertFixedSelection(result.selections.get(0), trackGroups, defaultOnly);
 
-    // With no language preference and no text track flagged as default, the first forced should be
+    // Default flags are disabled and no language preference is provided, so no text track is
     // selected.
-    trackGroups = wrapFormats(forcedOnly, noFlag);
-    result = trackSelector.selectTracks(textRendererCapabilities, trackGroups, periodId, TIMELINE);
-    assertFixedSelection(result.selections.get(0), trackGroups, forcedOnly);
-
-    // Default flags are disabled, so the first track flagged as forced should be selected.
     trackGroups = wrapFormats(defaultOnly, noFlag, forcedOnly, forcedDefault);
     trackSelector.setParameters(
         Parameters.DEFAULT
@@ -924,15 +919,7 @@ public final class DefaultTrackSelectorTest {
             .setDisabledTextTrackSelectionFlags(C.SELECTION_FLAG_DEFAULT)
             .build());
     result = trackSelector.selectTracks(textRendererCapabilities, trackGroups, periodId, TIMELINE);
-    assertFixedSelection(result.selections.get(0), trackGroups, forcedOnly);
+    assertNoSelection(result.selections.get(0));
-
-    // Default flags are disabled, but there is a text track flagged as forced whose language
-    // matches the preferred audio language.
-    trackGroups = wrapFormats(forcedDefault, forcedOnly, defaultOnly, noFlag, forcedOnlySpanish);
-    trackSelector.setParameters(
-        trackSelector.getParameters().buildUpon().setPreferredTextLanguage("spa").build());
-    result = trackSelector.selectTracks(textRendererCapabilities, trackGroups, periodId, TIMELINE);
-    assertFixedSelection(result.selections.get(0), trackGroups, forcedOnlySpanish);
 
     // All selection flags are disabled and there is no language preference, so nothing should be
     // selected.
@@ -977,6 +964,11 @@ public final class DefaultTrackSelectorTest {
         buildTextFormat(/* id= */ "forcedEnglish", /* language= */ "eng", C.SELECTION_FLAG_FORCED);
     Format forcedGerman =
         buildTextFormat(/* id= */ "forcedGerman", /* language= */ "deu", C.SELECTION_FLAG_FORCED);
+    Format forcedNoLanguage =
+        buildTextFormat(
+            /* id= */ "forcedNoLanguage",
+            /* language= */ C.LANGUAGE_UNDETERMINED,
+            C.SELECTION_FLAG_FORCED);
     Format audio = buildAudioFormat(/* id= */ "audio");
     Format germanAudio =
         buildAudioFormat(
@@ -994,16 +986,18 @@ public final class DefaultTrackSelectorTest {
           ALL_TEXT_FORMAT_SUPPORTED_RENDERER_CAPABILITIES
         };
 
-    // The audio declares no language. The first forced text track should be selected.
+    // Neither the audio nor the forced text track define a language. We select them both under the
-    TrackGroupArray trackGroups = wrapFormats(audio, forcedEnglish, forcedGerman);
+    // assumption that they have matching language.
+    TrackGroupArray trackGroups = wrapFormats(audio, forcedNoLanguage);
     TrackSelectorResult result =
         trackSelector.selectTracks(rendererCapabilities, trackGroups, periodId, TIMELINE);
-    assertFixedSelection(result.selections.get(1), trackGroups, forcedEnglish);
+    assertFixedSelection(result.selections.get(1), trackGroups, forcedNoLanguage);
 
-    // Ditto.
+    // No forced text track should be selected because none of the forced text tracks' languages
-    trackGroups = wrapFormats(audio, forcedGerman, forcedEnglish);
+    // matches the selected audio language.
+    trackGroups = wrapFormats(audio, forcedEnglish, forcedGerman);
     result = trackSelector.selectTracks(rendererCapabilities, trackGroups, periodId, TIMELINE);
-    assertFixedSelection(result.selections.get(1), trackGroups, forcedGerman);
+    assertNoSelection(result.selections.get(1));
 
     // The audio declares german. The german forced track should be selected.
     trackGroups = wrapFormats(germanAudio, forcedGerman, forcedEnglish);