Use system Locale language to select audio track.

If no track matches the preferred language or no preferred language is provided,
use the system Locale language as the next decision criterion.

PiperOrigin-RevId: 241322703

RELEASENOTES.md

@@ -90,6 +90,7 @@
 * Prevent seeking when ICY metadata is present to prevent playback problems
   ([#5658](https://github.com/google/ExoPlayer/issues/5658)).
 * Use full BCP 47 language tags in `Format`.
+* Select audio track based on system language if no preference is provided.
 
 ### 2.9.6 ###
 

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

@@ -2073,23 +2073,23 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           if (languageScore > 0
               || (params.selectUndeterminedTextLanguage && formatHasNoLanguage(format))) {
             if (isDefault) {
-              trackScore = 13;
+              trackScore = 17;
             } 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 = 10;
+              trackScore = 13;
             } else {
-              trackScore = 7;
+              trackScore = 9;
             }
             trackScore += languageScore;
           } else if (isDefault) {
-            trackScore = 6;
+            trackScore = 8;
           } else if (isForced) {
             int preferredAudioLanguageScore =
                 getFormatLanguageScore(format, params.preferredAudioLanguage);
             if (preferredAudioLanguageScore > 0) {
-              trackScore = 3 + preferredAudioLanguageScore;
+              trackScore = 4 + preferredAudioLanguageScore;
             } else {
               trackScore = 1 + getFormatLanguageScore(format, selectedAudioLanguage);
             }
@@ -2293,21 +2293,32 @@ public class DefaultTrackSelector extends MappingTrackSelector {
   }
 
   /**
-   * Returns a score for how well a language specified in a {@link Format} fits a given language.
+   * Returns a score for how well a language specified in a {@link Format} matches a given language.
    *
    * @param format The {@link Format}.
    * @param language The language, or null.
-   * @return A score of 0 if the languages don't fit, a score of 1 if the languages fit partly and a
-   *     score of 2 if the languages fit fully.
+   * @return A score of 3 if the languages match fully, a score of 2 if the languages match partly,
+   *     a score of 1 if the languages don't match but belong to the same main language, and a score
+   *     of 0 if the languages don't match at all.
    */
   protected static int getFormatLanguageScore(Format format, @Nullable String language) {
-    if (language == null) {
+    if (format.language == null || language == null) {
       return 0;
     }
-    if (TextUtils.equals(language, format.language)) {
+    if (TextUtils.equals(format.language, language)) {
+      return 3;
+    }
+    // Partial match where one language is a subset of the other (e.g. "zho-hans" and "zho-hans-hk")
+    if (format.language.startsWith(language) || language.startsWith(format.language)) {
       return 2;
     }
-    return format.language != null && format.language.startsWith(language) ? 1 : 0;
+    // Partial match where only the main language tag is the same (e.g. "fra-fr" and "fra-ca")
+    if (format.language.length() >= 3
+        && language.length() >= 3
+        && format.language.substring(0, 3).equals(language.substring(0, 3))) {
+      return 1;
+    }
+    return 0;
   }
 
   private static List<Integer> getViewportFilteredTrackIndices(TrackGroup group, int viewportWidth,
@@ -2385,18 +2396,20 @@ public class DefaultTrackSelector extends MappingTrackSelector {
     public final boolean isWithinConstraints;
 
     private final Parameters parameters;
-    private final int withinRendererCapabilitiesScore;
-    private final int matchLanguageScore;
-    private final int defaultSelectionFlagScore;
+    private final boolean isWithinRendererCapabilities;
+    private final int preferredLanguageScore;
+    private final int localeLanguageMatchIndex;
+    private final int localeLanguageScore;
+    private final boolean isDefaultSelectionFlag;
     private final int channelCount;
     private final int sampleRate;
     private final int bitrate;
 
     public AudioTrackScore(Format format, Parameters parameters, int formatSupport) {
       this.parameters = parameters;
-      withinRendererCapabilitiesScore = isSupported(formatSupport, false) ? 1 : 0;
-      matchLanguageScore = getFormatLanguageScore(format, parameters.preferredAudioLanguage);
-      defaultSelectionFlagScore = (format.selectionFlags & C.SELECTION_FLAG_DEFAULT) != 0 ? 1 : 0;
+      isWithinRendererCapabilities = isSupported(formatSupport, false);
+      preferredLanguageScore = getFormatLanguageScore(format, parameters.preferredAudioLanguage);
+      isDefaultSelectionFlag = (format.selectionFlags & C.SELECTION_FLAG_DEFAULT) != 0;
       channelCount = format.channelCount;
       sampleRate = format.sampleRate;
       bitrate = format.bitrate;
@@ -2404,6 +2417,19 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           (format.bitrate == Format.NO_VALUE || format.bitrate <= parameters.maxAudioBitrate)
               && (format.channelCount == Format.NO_VALUE
                   || format.channelCount <= parameters.maxAudioChannelCount);
+      String[] localeLanguages = Util.getSystemLanguageCodes();
+      int bestMatchIndex = Integer.MAX_VALUE;
+      int bestMatchScore = 0;
+      for (int i = 0; i < localeLanguages.length; i++) {
+        int score = getFormatLanguageScore(format, localeLanguages[i]);
+        if (score > 0) {
+          bestMatchIndex = i;
+          bestMatchScore = score;
+          break;
+        }
+      }
+      localeLanguageMatchIndex = bestMatchIndex;
+      localeLanguageScore = bestMatchScore;
     }
 
     /**
@@ -2415,12 +2441,11 @@ public class DefaultTrackSelector extends MappingTrackSelector {
      */
     @Override
     public int compareTo(@NonNull AudioTrackScore other) {
-      if (this.withinRendererCapabilitiesScore != other.withinRendererCapabilitiesScore) {
-        return compareInts(this.withinRendererCapabilitiesScore,
-            other.withinRendererCapabilitiesScore);
+      if (this.isWithinRendererCapabilities != other.isWithinRendererCapabilities) {
+        return this.isWithinRendererCapabilities ? 1 : -1;
       }
-      if (this.matchLanguageScore != other.matchLanguageScore) {
-        return compareInts(this.matchLanguageScore, other.matchLanguageScore);
+      if (this.preferredLanguageScore != other.preferredLanguageScore) {
+        return compareInts(this.preferredLanguageScore, other.preferredLanguageScore);
       }
       if (this.isWithinConstraints != other.isWithinConstraints) {
         return this.isWithinConstraints ? 1 : -1;
@@ -2431,12 +2456,18 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           return bitrateComparison > 0 ? -1 : 1;
         }
       }
-      if (this.defaultSelectionFlagScore != other.defaultSelectionFlagScore) {
-        return compareInts(this.defaultSelectionFlagScore, other.defaultSelectionFlagScore);
+      if (this.isDefaultSelectionFlag != other.isDefaultSelectionFlag) {
+        return this.isDefaultSelectionFlag ? 1 : -1;
+      }
+      if (this.localeLanguageMatchIndex != other.localeLanguageMatchIndex) {
+        return -compareInts(this.localeLanguageMatchIndex, other.localeLanguageMatchIndex);
+      }
+      if (this.localeLanguageScore != other.localeLanguageScore) {
+        return compareInts(this.localeLanguageScore, other.localeLanguageScore);
       }
       // If the formats are within constraints and renderer capabilities then prefer higher values
       // of channel count, sample rate and bit rate in that order. Otherwise, prefer lower values.
-      int resultSign = isWithinConstraints && withinRendererCapabilitiesScore == 1 ? 1 : -1;
+      int resultSign = isWithinConstraints && isWithinRendererCapabilities ? 1 : -1;
       if (this.channelCount != other.channelCount) {
         return resultSign * compareInts(this.channelCount, other.channelCount);
       }

library/core/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -29,6 +29,7 @@ import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.content.res.Configuration;
+import android.content.res.Resources;
 import android.graphics.Point;
 import android.media.AudioFormat;
 import android.net.ConnectivityManager;
@@ -445,18 +446,18 @@ public final class Util {
    * @return The all-lowercase normalized code, or null if the input was null, or {@code
    *     language.toLowerCase()} if the language could not be normalized.
    */
-  public static @Nullable String normalizeLanguageCode(@Nullable String language) {
+  public static @PolyNull String normalizeLanguageCode(@PolyNull String language) {
     if (language == null) {
       return null;
     }
     try {
-      Locale locale = Util.SDK_INT >= 21 ? Locale.forLanguageTag(language) : new Locale(language);
+      Locale locale = getLocaleForLanguageTag(language);
       int localeLanguageLength = locale.getLanguage().length();
       String normLanguage = locale.getISO3Language();
       if (normLanguage.isEmpty()) {
         return toLowerInvariant(language);
       }
-      String normTag = Util.SDK_INT >= 21 ? locale.toLanguageTag() : locale.toString();
+      String normTag = getLocaleLanguageTag(locale);
       return toLowerInvariant(normLanguage + normTag.substring(localeLanguageLength));
     } catch (MissingResourceException e) {
       return toLowerInvariant(language);
@@ -1754,6 +1755,18 @@ public final class Util {
   }
 
   /**
+   * Returns a non-empty array of normalized IETF BCP 47 language tags for the system languages
+   * ordered by preference.
+   */
+  public static String[] getSystemLanguageCodes() {
+    String[] systemLocales = getSystemLocales();
+    for (int i = 0; i < systemLocales.length; i++) {
+      systemLocales[i] = normalizeLanguageCode(systemLocales[i]);
+    }
+    return systemLocales;
+  }
+
+  /**
    * Uncompresses the data in {@code input}.
    *
    * @param input Wraps the compressed input data.
@@ -1936,6 +1949,35 @@ public final class Util {
     display.getSize(outSize);
   }
 
+  private static String[] getSystemLocales() {
+    return SDK_INT >= 24
+        ? getSystemLocalesV24()
+        : new String[] {getLocaleLanguageTag(Resources.getSystem().getConfiguration().locale)};
+  }
+
+  @TargetApi(24)
+  private static String[] getSystemLocalesV24() {
+    return Util.split(Resources.getSystem().getConfiguration().getLocales().toLanguageTags(), ",");
+  }
+
+  private static Locale getLocaleForLanguageTag(String languageTag) {
+    return Util.SDK_INT >= 21 ? getLocaleForLanguageTagV21(languageTag) : new Locale(languageTag);
+  }
+
+  @TargetApi(21)
+  private static Locale getLocaleForLanguageTagV21(String languageTag) {
+    return Locale.forLanguageTag(languageTag);
+  }
+
+  private static String getLocaleLanguageTag(Locale locale) {
+    return SDK_INT >= 21 ? getLocaleLanguageTagV21(locale) : locale.toString();
+  }
+
+  @TargetApi(21)
+  private static String getLocaleLanguageTagV21(Locale locale) {
+    return locale.toLanguageTag();
+  }
+
   private static @C.NetworkType int getMobileNetworkType(NetworkInfo networkInfo) {
     switch (networkInfo.getSubtype()) {
       case TelephonyManager.NETWORK_TYPE_EDGE: