Add allowAudioMixedChannelCountAdaptiveness parameter to DefaultTrackSelector.

We already allow mixed mime type and mixed sample rate adaptation on request,
so for completeness, we can also allow mixed channel count adaptation.

Issue:#6257
PiperOrigin-RevId: 261930046

RELEASENOTES.md

 # Release notes #
 # Release notes #
 
 
+### 2.10.5 ###
+
+* Add `allowAudioMixedChannelCountAdaptiveness` parameter to
+  `DefaultTrackSelector` to allow adaptive selections of audio tracks with
+  different channel counts
+  ([#6257](https://github.com/google/ExoPlayer/issues/6257)).
+
 ### 2.10.4 ###
 ### 2.10.4 ###
 
 
 * Offline: Add `Scheduler` implementation that uses `WorkManager`.
 * Offline: Add `Scheduler` implementation that uses `WorkManager`.

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

@@ -143,6 +143,7 @@ public final class DefaultTrackSelectorTest {
             /* exceedAudioConstraintsIfNecessary= */ false,
             /* exceedAudioConstraintsIfNecessary= */ false,
             /* allowAudioMixedMimeTypeAdaptiveness= */ true,
             /* allowAudioMixedMimeTypeAdaptiveness= */ true,
             /* allowAudioMixedSampleRateAdaptiveness= */ false,
             /* allowAudioMixedSampleRateAdaptiveness= */ false,
+            /* allowAudioMixedChannelCountAdaptiveness= */ true,
             // Text
             // Text
             /* preferredTextLanguage= */ "de",
             /* preferredTextLanguage= */ "de",
             /* selectUndeterminedTextLanguage= */ true,
             /* selectUndeterminedTextLanguage= */ true,