Ensure HlsMediaPeriod works with playlists without variants.

Currently, we remove all variants if none of the stream keys contains any
variants. This causes HlsMediaPeriod to throw exceptions as it expects at least
one variant.

Change it to support master playlists without variants.

PiperOrigin-RevId: 231385547

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaPeriod.java

@@ -343,15 +343,19 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
 
   private void buildAndPrepareSampleStreamWrappers(long positionUs) {
     HlsMasterPlaylist masterPlaylist = playlistTracker.getMasterPlaylist();
+    boolean hasVariants = !masterPlaylist.variants.isEmpty();
     List<HlsUrl> audioRenditions = masterPlaylist.audios;
     List<HlsUrl> subtitleRenditions = masterPlaylist.subtitles;
 
-    int wrapperCount = 1 /* variants */ + audioRenditions.size() + subtitleRenditions.size();
+    int wrapperCount = (hasVariants ? 1 : 0) + audioRenditions.size() + subtitleRenditions.size();
     sampleStreamWrappers = new HlsSampleStreamWrapper[wrapperCount];
     pendingPrepareCount = wrapperCount;
 
-    buildAndPrepareMainSampleStreamWrapper(masterPlaylist, positionUs);
-    int currentWrapperIndex = 1;
+    int currentWrapperIndex = 0;
+    if (hasVariants) {
+      buildAndPrepareMainSampleStreamWrapper(masterPlaylist, positionUs);
+      currentWrapperIndex++;
+    }
 
     // TODO: Build video stream wrappers here.
 
@@ -370,8 +374,6 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
       if (allowChunklessPreparation && renditionFormat.codecs != null) {
         sampleStreamWrapper.prepareWithMasterPlaylistInfo(
             new TrackGroupArray(new TrackGroup(audioRendition.format)), 0, TrackGroupArray.EMPTY);
-      } else {
-        sampleStreamWrapper.continuePreparing();
       }
     }
 
@@ -386,6 +388,12 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
           new TrackGroupArray(new TrackGroup(url.format)), 0, TrackGroupArray.EMPTY);
     }
 
+    // Set timestamp master and trigger preparation (if not already prepared)
+    sampleStreamWrappers[0].setIsTimestampMaster(true);
+    for (HlsSampleStreamWrapper sampleStreamWrapper : sampleStreamWrappers) {
+      sampleStreamWrapper.continuePreparing();
+    }
+
     // All wrappers are enabled during preparation.
     enabledSampleStreamWrappers = sampleStreamWrappers;
   }
@@ -503,9 +511,6 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
           new TrackGroupArray(muxedTrackGroups.toArray(new TrackGroup[0])),
           0,
           new TrackGroupArray(id3TrackGroup));
-    } else {
-      sampleStreamWrapper.setIsTimestampMaster(true);
-      sampleStreamWrapper.continuePreparing();
     }
   }
 
@@ -566,7 +571,7 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
       if (isPrimaryTrackInVariant) {
         channelCount = variantFormat.channelCount;
         selectionFlags = variantFormat.selectionFlags;
-        language = variantFormat.label;
+        language = variantFormat.language;
         label = variantFormat.label;
       }
     }