DASH: Stop interpreting `main` track role as `SELECTION_FLAG_DEFAULT`

The `main` role distinguishes a track from an `alternate`, but unlike
`SELECTION_FLAG_DEFAULT` it doesn't imply the track should be selected
unless user preferences state otherwise. e.g. in the case of a text
track, the player shouldn't enable subtitle rendering just because a
`main` text track is present in the manifest.

The `main`/`alternate` distinction is still available through
`Format.roleFlags` and the `ROLE_FLAG_MAIN` and `ROLE_FLAG_ALTERNATE`
values.

This behaviour was originally [added in 2.2.0](https://github.com/google/ExoPlayer/commit/7f967f305718bc2c9ee679fdd7d014eccef0356b),
however at the time the `C.RoleFlags` IntDef did not exist. The IntDef
was [added in 2.10.0](https://github.com/google/ExoPlayer/commit/a86a9137be5f0ed89de3d68f4c4800a7753cc881).

PiperOrigin-RevId: 418937747

RELEASENOTES.md

@@ -59,6 +59,7 @@
 *   DASH:
     *   Support the `forced-subtitle` track role
         ([#9727](https://github.com/google/ExoPlayer/issues/9727)).
+    *   Stop interpreting the `main` track role as `C.SELECTION_FLAG_DEFAULT`.
 *   HLS:
     *   Use chunkless preparation by default to improve start up time. If your
         renditions contain muxed closed-caption tracks that are *not* declared

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/manifest/DashManifestParser.java

@@ -1472,8 +1472,6 @@ public class DashManifestParser extends DefaultHandler
       return 0;
     }
     switch (value) {
-      case "main":
-        return C.SELECTION_FLAG_DEFAULT;
       case "forced_subtitle":
         // Support both hyphen and underscore (https://github.com/google/ExoPlayer/issues/9727).
       case "forced-subtitle":

library/dash/src/test/java/com/google/android/exoplayer2/source/dash/manifest/DashManifestParserTest.java

@@ -243,7 +243,8 @@ public class DashManifestParserTest {
     assertThat(format.containerMimeType).isEqualTo(MimeTypes.APPLICATION_RAWCC);
     assertThat(format.sampleMimeType).isEqualTo(MimeTypes.APPLICATION_CEA608);
     assertThat(format.codecs).isEqualTo("cea608");
-    assertThat(format.roleFlags).isEqualTo(C.ROLE_FLAG_SUBTITLE);
+    assertThat(format.roleFlags).isEqualTo(C.ROLE_FLAG_SUBTITLE | C.ROLE_FLAG_MAIN);
+    assertThat(format.selectionFlags).isEqualTo(0);
     assertThat(adaptationSets.get(0).type).isEqualTo(C.TRACK_TYPE_TEXT);
 
     format = adaptationSets.get(1).representations.get(0).format;

testdata/src/test/assets/media/mpd/sample_mpd_text

@@ -8,6 +8,7 @@
   </SegmentTemplate>
   <AdaptationSet id="0" mimeType="application/x-rawcc" subsegmentAlignment="true">
    <Role schemeIdUri="urn:mpeg:DASH:role:2011" value="subtitle"/>
+   <Role schemeIdUri="urn:mpeg:DASH:role:2011" value="main"/>
    <Representation id="0" codecs="cea608" bandwidth="16">
     <BaseURL>https://test.com/0</BaseURL>
    </Representation>