Don't allow spliced-in preload chunks.

Preload chunks may still need to be discarded. However, we don't
currently support discarding spliced-in chunks. Thus, we need to
avoid loadng a preload chunk that needs to be spliced-in.

Issue: #8937

#minor-release

PiperOrigin-RevId: 374851661

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

@@ -352,70 +352,67 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       return;
     }
     @Nullable
-    HlsMediaPlaylist mediaPlaylist =
+    HlsMediaPlaylist playlist =
         playlistTracker.getPlaylistSnapshot(selectedPlaylistUrl, /* isForPlayback= */ true);
-    // playlistTracker snapshot is valid (checked by if() above), so mediaPlaylist must be non-null.
-    checkNotNull(mediaPlaylist);
-    independentSegments = mediaPlaylist.hasIndependentSegments;
+    // playlistTracker snapshot is valid (checked by if() above), so playlist must be non-null.
+    checkNotNull(playlist);
+    independentSegments = playlist.hasIndependentSegments;
 
-    updateLiveEdgeTimeUs(mediaPlaylist);
+    updateLiveEdgeTimeUs(playlist);
 
     // Select the chunk.
-    long startOfPlaylistInPeriodUs =
-        mediaPlaylist.startTimeUs - playlistTracker.getInitialStartTimeUs();
+    long startOfPlaylistInPeriodUs = playlist.startTimeUs - playlistTracker.getInitialStartTimeUs();
     Pair<Long, Integer> nextMediaSequenceAndPartIndex =
         getNextMediaSequenceAndPartIndex(
-            previous, switchingTrack, mediaPlaylist, startOfPlaylistInPeriodUs, loadPositionUs);
+            previous, switchingTrack, playlist, startOfPlaylistInPeriodUs, loadPositionUs);
     long chunkMediaSequence = nextMediaSequenceAndPartIndex.first;
     int partIndex = nextMediaSequenceAndPartIndex.second;
-    if (chunkMediaSequence < mediaPlaylist.mediaSequence && previous != null && switchingTrack) {
+    if (chunkMediaSequence < playlist.mediaSequence && previous != null && switchingTrack) {
       // We try getting the next chunk without adapting in case that's the reason for falling
       // behind the live window.
       selectedTrackIndex = oldTrackIndex;
       selectedPlaylistUrl = playlistUrls[selectedTrackIndex];
-      mediaPlaylist =
+      playlist =
           playlistTracker.getPlaylistSnapshot(selectedPlaylistUrl, /* isForPlayback= */ true);
-      // playlistTracker snapshot is valid (checked by if() above), so mediaPlaylist must be
-      // non-null.
-      checkNotNull(mediaPlaylist);
-      startOfPlaylistInPeriodUs =
-          mediaPlaylist.startTimeUs - playlistTracker.getInitialStartTimeUs();
+      // playlistTracker snapshot is valid (checked by if() above), so playlist must be non-null.
+      checkNotNull(playlist);
+      startOfPlaylistInPeriodUs = playlist.startTimeUs - playlistTracker.getInitialStartTimeUs();
       // Get the next segment/part without switching tracks.
       Pair<Long, Integer> nextMediaSequenceAndPartIndexWithoutAdapting =
           getNextMediaSequenceAndPartIndex(
               previous,
               /* switchingTrack= */ false,
-              mediaPlaylist,
+              playlist,
               startOfPlaylistInPeriodUs,
               loadPositionUs);
       chunkMediaSequence = nextMediaSequenceAndPartIndexWithoutAdapting.first;
       partIndex = nextMediaSequenceAndPartIndexWithoutAdapting.second;
     }
 
-    if (chunkMediaSequence < mediaPlaylist.mediaSequence) {
+    if (chunkMediaSequence < playlist.mediaSequence) {
       fatalError = new BehindLiveWindowException();
       return;
     }
 
     @Nullable
     SegmentBaseHolder segmentBaseHolder =
-        getNextSegmentHolder(mediaPlaylist, chunkMediaSequence, partIndex);
+        getNextSegmentHolder(playlist, chunkMediaSequence, partIndex);
     if (segmentBaseHolder == null) {
-      if (!mediaPlaylist.hasEndTag) {
+      if (!playlist.hasEndTag) {
         // Reload the playlist in case of a live stream.
         out.playlistUrl = selectedPlaylistUrl;
         seenExpectedPlaylistError &= selectedPlaylistUrl.equals(expectedPlaylistUrl);
         expectedPlaylistUrl = selectedPlaylistUrl;
         return;
-      } else if (allowEndOfStream || mediaPlaylist.segments.isEmpty()) {
+      } else if (allowEndOfStream || playlist.segments.isEmpty()) {
         out.endOfStream = true;
         return;
       }
       // Use the last segment available in case of a VOD stream.
       segmentBaseHolder =
           new SegmentBaseHolder(
-              Iterables.getLast(mediaPlaylist.segments),
-              mediaPlaylist.mediaSequence + mediaPlaylist.segments.size() - 1,
+              Iterables.getLast(playlist.segments),
+              playlist.mediaSequence + playlist.segments.size() - 1,
               /* partIndex= */ C.INDEX_UNSET);
     }
 
@@ -426,24 +423,36 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     // Check if the media segment or its initialization segment are fully encrypted.
     @Nullable
     Uri initSegmentKeyUri =
-        getFullEncryptionKeyUri(mediaPlaylist, segmentBaseHolder.segmentBase.initializationSegment);
+        getFullEncryptionKeyUri(playlist, segmentBaseHolder.segmentBase.initializationSegment);
     out.chunk = maybeCreateEncryptionChunkFor(initSegmentKeyUri, selectedTrackIndex);
     if (out.chunk != null) {
       return;
     }
     @Nullable
-    Uri mediaSegmentKeyUri = getFullEncryptionKeyUri(mediaPlaylist, segmentBaseHolder.segmentBase);
+    Uri mediaSegmentKeyUri = getFullEncryptionKeyUri(playlist, segmentBaseHolder.segmentBase);
     out.chunk = maybeCreateEncryptionChunkFor(mediaSegmentKeyUri, selectedTrackIndex);
     if (out.chunk != null) {
       return;
     }
+
+    boolean shouldSpliceIn =
+        HlsMediaChunk.shouldSpliceIn(
+            previous, selectedPlaylistUrl, playlist, segmentBaseHolder, startOfPlaylistInPeriodUs);
+    if (shouldSpliceIn && segmentBaseHolder.isPreload) {
+      // We don't support discarding spliced-in segments [internal: b/159904763], but preload
+      // parts may need to be discarded if they are removed before becoming permanently published.
+      // Hence, don't allow this combination and instead wait with loading the next part until it
+      // becomes fully available (or the track selection selects another track).
+      return;
+    }
+
     out.chunk =
         HlsMediaChunk.createInstance(
             extractorFactory,
             mediaDataSource,
             playlistFormats[selectedTrackIndex],
             startOfPlaylistInPeriodUs,
-            mediaPlaylist,
+            playlist,
             segmentBaseHolder,
             selectedPlaylistUrl,
             muxedCaptionFormats,
@@ -453,7 +462,8 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
             timestampAdjusterProvider,
             previous,
             /* mediaSegmentKey= */ keyCache.get(mediaSegmentKeyUri),
-            /* initSegmentKey= */ keyCache.get(initSegmentKeyUri));
+            /* initSegmentKey= */ keyCache.get(initSegmentKeyUri),
+            shouldSpliceIn);
   }
 
   @Nullable

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

@@ -75,6 +75,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    * @param mediaSegmentKey The media segment decryption key, if fully encrypted. Null otherwise.
    * @param initSegmentKey The initialization segment decryption key, if fully encrypted. Null
    *     otherwise.
+   * @param shouldSpliceIn Whether samples for this chunk should be spliced into existing samples.
    */
   public static HlsMediaChunk createInstance(
       HlsExtractorFactory extractorFactory,
@@ -91,7 +92,8 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       TimestampAdjusterProvider timestampAdjusterProvider,
       @Nullable HlsMediaChunk previousChunk,
       @Nullable byte[] mediaSegmentKey,
-      @Nullable byte[] initSegmentKey) {
+      @Nullable byte[] initSegmentKey,
+      boolean shouldSpliceIn) {
     // Media segment.
     HlsMediaPlaylist.SegmentBase mediaSegment = segmentBaseHolder.segmentBase;
     DataSpec dataSpec =
@@ -135,17 +137,12 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     @Nullable HlsMediaChunkExtractor previousExtractor = null;
     Id3Decoder id3Decoder;
     ParsableByteArray scratchId3Data;
-    boolean shouldSpliceIn;
+
     if (previousChunk != null) {
       boolean isFollowingChunk =
           playlistUrl.equals(previousChunk.playlistUrl) && previousChunk.loadCompleted;
       id3Decoder = previousChunk.id3Decoder;
       scratchId3Data = previousChunk.scratchId3Data;
-      boolean isIndependent = isIndependent(segmentBaseHolder, mediaPlaylist);
-      boolean canContinueWithoutSplice =
-          isFollowingChunk
-              || (isIndependent && segmentStartTimeInPeriodUs >= previousChunk.endTimeUs);
-      shouldSpliceIn = !canContinueWithoutSplice;
       previousExtractor =
           isFollowingChunk
                   && !previousChunk.extractorInvalidated
@@ -155,7 +152,6 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     } else {
       id3Decoder = new Id3Decoder();
       scratchId3Data = new ParsableByteArray(Id3Decoder.ID3_HEADER_LENGTH);
-      shouldSpliceIn = false;
     }
     return new HlsMediaChunk(
         extractorFactory,
@@ -186,6 +182,41 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
         shouldSpliceIn);
   }
 
+  /**
+   * Returns whether samples of a new HLS media chunk should be spliced into existing samples.
+   *
+   * @param previousChunk The previous existing media chunk, or null if the new chunk is the first
+   *     in the queue.
+   * @param playlistUrl The URL of the playlist from which the new chunk will be obtained.
+   * @param mediaPlaylist The {@link HlsMediaPlaylist} containing the new chunk.
+   * @param segmentBaseHolder The {@link HlsChunkSource.SegmentBaseHolder} with information about
+   *     the new chunk.
+   * @param startOfPlaylistInPeriodUs The start time of the playlist in the period, in microseconds.
+   * @return Whether samples of the new chunk should be spliced into existing samples.
+   */
+  public static boolean shouldSpliceIn(
+      @Nullable HlsMediaChunk previousChunk,
+      Uri playlistUrl,
+      HlsMediaPlaylist mediaPlaylist,
+      HlsChunkSource.SegmentBaseHolder segmentBaseHolder,
+      long startOfPlaylistInPeriodUs) {
+    if (previousChunk == null) {
+      // First chunk doesn't require splicing.
+      return false;
+    }
+    if (playlistUrl.equals(previousChunk.playlistUrl) && previousChunk.loadCompleted) {
+      // Continuing with the next chunk in the same playlist after fully loading the previous chunk
+      // (i.e. the load wasn't cancelled or failed) is always possible.
+      return false;
+    }
+    // Changing playlists or continuing after a chunk cancellation/failure requires independent,
+    // non-overlapping segments to avoid the splice.
+    long segmentStartTimeInPeriodUs =
+        startOfPlaylistInPeriodUs + segmentBaseHolder.segmentBase.relativeStartTimeUs;
+    return !isIndependent(segmentBaseHolder, mediaPlaylist)
+        || segmentStartTimeInPeriodUs < previousChunk.endTimeUs;
+  }
+
   public static final String PRIV_TIMESTAMP_FRAME_OWNER =
       "com.apple.streaming.transportStreamTimestamp";
 

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

@@ -709,6 +709,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
               ? lastMediaChunk.endTimeUs
               : max(lastSeekPositionUs, lastMediaChunk.startTimeUs);
     }
+    nextChunkHolder.clear();
     chunkSource.getNextChunk(
         positionUs,
         loadPositionUs,
@@ -718,7 +719,6 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     boolean endOfStream = nextChunkHolder.endOfStream;
     @Nullable Chunk loadable = nextChunkHolder.chunk;
     @Nullable Uri playlistUrlToLoad = nextChunkHolder.playlistUrl;
-    nextChunkHolder.clear();
 
     if (endOfStream) {
       pendingResetPositionUs = C.TIME_UNSET;