Update track selection to prefer content over technical preferences.

Currently we prefer technical preferences set in the Parameters over
content preferences implied by the media. It proably makes more
sense in the opposite order to avoid the situation where a
non-default track (e.g. commentary) is selected just because it
better matches some technical criteria.

Also add comments explaining the track selection logic stages.

PiperOrigin-RevId: 412840962

RELEASENOTES.md

@@ -5,6 +5,10 @@
 *   Core library:
     *   Support preferred video role flags in track selection
         ((#9402)[https://github.com/google/ExoPlayer/issues/9402]).
+    *   Prefer audio content preferences (for example, "default" audio track or
+        track matching system Locale language) over technical track selection
+        constraints (for example, preferred MIME type, or maximum channel
+        count).
 *   Extractors:
     *   Fix inconsistency with spec in H.265 SPS nal units parsing
         ((#9719)[https://github.com/google/ExoPlayer/issues/9719]).

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

@@ -2558,14 +2558,18 @@ public class DefaultTrackSelector extends MappingTrackSelector {
               : FORMAT_VALUE_ORDERING.reverse();
       return ComparisonChain.start()
           .compareFalseFirst(this.isWithinRendererCapabilities, other.isWithinRendererCapabilities)
+          // 1. Compare match with specific content preferences set by the parameters.
           .compare(this.preferredRoleFlagsScore, other.preferredRoleFlagsScore)
+          // 2. Compare match with implicit content preferences set by the media.
           .compareFalseFirst(this.hasMainOrNoRoleFlag, other.hasMainOrNoRoleFlag)
+          // 3. Compare match with technical preferences set by the parameters.
           .compareFalseFirst(this.isWithinMaxConstraints, other.isWithinMaxConstraints)
           .compareFalseFirst(this.isWithinMinConstraints, other.isWithinMinConstraints)
           .compare(
               this.preferredMimeTypeMatchIndex,
               other.preferredMimeTypeMatchIndex,
               Ordering.natural().reverse())
+          // 4. Compare technical quality.
           .compare(
               this.bitrate,
               other.bitrate,
@@ -2675,13 +2679,22 @@ public class DefaultTrackSelector extends MappingTrackSelector {
               : FORMAT_VALUE_ORDERING.reverse();
       return ComparisonChain.start()
           .compareFalseFirst(this.isWithinRendererCapabilities, other.isWithinRendererCapabilities)
+          // 1. Compare match with specific content preferences set by the parameters.
           .compare(
               this.preferredLanguageIndex,
               other.preferredLanguageIndex,
               Ordering.natural().reverse())
           .compare(this.preferredLanguageScore, other.preferredLanguageScore)
           .compare(this.preferredRoleFlagsScore, other.preferredRoleFlagsScore)
+          // 2. Compare match with implicit content preferences set by the media or the system.
+          .compareFalseFirst(this.isDefaultSelectionFlag, other.isDefaultSelectionFlag)
           .compareFalseFirst(this.hasMainOrNoRoleFlag, other.hasMainOrNoRoleFlag)
+          .compare(
+              this.localeLanguageMatchIndex,
+              other.localeLanguageMatchIndex,
+              Ordering.natural().reverse())
+          .compare(this.localeLanguageScore, other.localeLanguageScore)
+          // 3. Compare match with technical preferences set by the parameters.
           .compareFalseFirst(this.isWithinConstraints, other.isWithinConstraints)
           .compare(
               this.preferredMimeTypeMatchIndex,
@@ -2691,12 +2704,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
               this.bitrate,
               other.bitrate,
               parameters.forceLowestBitrate ? FORMAT_VALUE_ORDERING.reverse() : NO_ORDER)
-          .compareFalseFirst(this.isDefaultSelectionFlag, other.isDefaultSelectionFlag)
-          .compare(
-              this.localeLanguageMatchIndex,
-              other.localeLanguageMatchIndex,
-              Ordering.natural().reverse())
-          .compare(this.localeLanguageScore, other.localeLanguageScore)
+          // 4. Compare technical quality.
           .compare(this.channelCount, other.channelCount, qualityOrdering)
           .compare(this.sampleRate, other.sampleRate, qualityOrdering)
           .compare(
@@ -2785,12 +2793,14 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           ComparisonChain.start()
               .compareFalseFirst(
                   this.isWithinRendererCapabilities, other.isWithinRendererCapabilities)
+              // 1. Compare match with specific content preferences set by the parameters.
               .compare(
                   this.preferredLanguageIndex,
                   other.preferredLanguageIndex,
                   Ordering.natural().reverse())
               .compare(this.preferredLanguageScore, other.preferredLanguageScore)
               .compare(this.preferredRoleFlagsScore, other.preferredRoleFlagsScore)
+              // 2. Compare match with implicit content preferences set by the media.
               .compareFalseFirst(this.isDefault, other.isDefault)
               .compare(
                   this.isForced,