From 805d3b763d25bf86e3c6c96a8e5f00ba32f2fc24 Mon Sep 17 00:00:00 2001
From: tonihei <tonihei@google.com>
Date: Mon, 29 Nov 2021 10:57:51 +0000
Subject: [PATCH] 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
---
 .../trackselection/DefaultTrackSelector.java  | 22 ++++++++++++++-----
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/trackselection/DefaultTrackSelector.java b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/trackselection/DefaultTrackSelector.java
index 757051ab49..9f18d407be 100644
--- a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/trackselection/DefaultTrackSelector.java
+++ b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/trackselection/DefaultTrackSelector.java
@@ -2566,14 +2566,18 @@ 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,
@@ -2683,13 +2687,22 @@ 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,
@@ -2699,12 +2712,7 @@ 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(
@@ -2793,12 +2801,14 @@ 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,