Make metadata field nullable in FlacStreamMetadata

This makes the format metadata null (instead of an empty Metadata
object) when it is not provided, and is therefore consistent with the
other extractors behavior.

PiperOrigin-RevId: 284171148

extensions/flac/src/androidTest/assets/bear.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
   total output bytes = 526272
   sample count = 33

extensions/flac/src/androidTest/assets/bear.flac.1.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
   total output bytes = 362432
   sample count = 23

extensions/flac/src/androidTest/assets/bear.flac.2.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
   total output bytes = 182208
   sample count = 12

extensions/flac/src/androidTest/assets/bear.flac.3.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
   total output bytes = 18368
   sample count = 2

extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/FlacExtractor.java

@@ -212,6 +212,7 @@ public final class FlacExtractor implements Extractor {
               input.getLength(),
               extractorOutput,
               outputFrameHolder);
+      @Nullable
       Metadata metadata = streamMetadata.getMetadataCopyWithAppendedEntriesFrom(id3Metadata);
       outputFormat(streamMetadata, metadata, trackOutput);
     }

library/core/src/main/java/com/google/android/exoplayer2/extractor/FlacMetadataReader.java

@@ -81,7 +81,8 @@ public final class FlacMetadataReader {
       throws IOException, InterruptedException {
     @Nullable
     Id3Decoder.FramePredicate id3FramePredicate = parseData ? null : Id3Decoder.NO_FRAMES_PREDICATE;
-    return new Id3Peeker().peekId3Data(input, id3FramePredicate);
+    @Nullable Metadata id3Metadata = new Id3Peeker().peekId3Data(input, id3FramePredicate);
+    return id3Metadata == null || id3Metadata.length() == 0 ? null : id3Metadata;
   }
 
   /**

library/core/src/main/java/com/google/android/exoplayer2/util/FlacStreamMetadata.java

@@ -80,8 +80,8 @@ public final class FlacStreamMetadata {
   /** Total number of samples, or 0 if the value is unknown. */
   public final long totalSamples;
 
-  /** Content metadata. */
+  /** Content metadata, or {@code null} if it is not provided. */
-  private final Metadata metadata;
+  @Nullable private final Metadata metadata;
 
   /**
    * Parses binary FLAC stream info metadata.
@@ -102,7 +102,7 @@ public final class FlacStreamMetadata {
     bitsPerSample = scratch.readBits(5) + 1;
     bitsPerSampleLookupKey = getBitsPerSampleLookupKey(bitsPerSample);
     totalSamples = scratch.readBitsToLong(36);
-    metadata = new Metadata();
+    metadata = null;
   }
 
   // Used in native code.
@@ -138,7 +138,7 @@ public final class FlacStreamMetadata {
       int channels,
       int bitsPerSample,
       long totalSamples,
-      Metadata metadata) {
+      @Nullable Metadata metadata) {
     this.minBlockSizeSamples = minBlockSizeSamples;
     this.maxBlockSizeSamples = maxBlockSizeSamples;
     this.minFrameSize = minFrameSize;
@@ -213,7 +213,7 @@ public final class FlacStreamMetadata {
     // Set the last metadata block flag, ignore the other blocks.
     streamMarkerAndInfoBlock[4] = (byte) 0x80;
     int maxInputSize = maxFrameSize > 0 ? maxFrameSize : Format.NO_VALUE;
-    Metadata metadataWithId3 = metadata.copyWithAppendedEntriesFrom(id3Metadata);
+    @Nullable Metadata metadataWithId3 = getMetadataCopyWithAppendedEntriesFrom(id3Metadata);
 
     return Format.createAudioSampleFormat(
         /* id= */ null,
@@ -234,14 +234,16 @@ public final class FlacStreamMetadata {
   }
 
   /** Returns a copy of the content metadata with entries from {@code other} appended. */
+  @Nullable
   public Metadata getMetadataCopyWithAppendedEntriesFrom(@Nullable Metadata other) {
-    return metadata.copyWithAppendedEntriesFrom(other);
+    return metadata == null ? other : metadata.copyWithAppendedEntriesFrom(other);
   }
 
   /** Returns a copy of {@code this} with the given Vorbis comments added to the metadata. */
   public FlacStreamMetadata copyWithVorbisComments(List<String> vorbisComments) {
+    @Nullable
     Metadata appendedMetadata =
-        metadata.copyWithAppendedEntriesFrom(
+        getMetadataCopyWithAppendedEntriesFrom(
             buildMetadata(vorbisComments, Collections.emptyList()));
     return new FlacStreamMetadata(
         minBlockSizeSamples,
@@ -257,8 +259,10 @@ public final class FlacStreamMetadata {
 
   /** Returns a copy of {@code this} with the given picture frames added to the metadata. */
   public FlacStreamMetadata copyWithPictureFrames(List<PictureFrame> pictureFrames) {
+    @Nullable
     Metadata appendedMetadata =
-        metadata.copyWithAppendedEntriesFrom(buildMetadata(Collections.emptyList(), pictureFrames));
+        getMetadataCopyWithAppendedEntriesFrom(
+            buildMetadata(Collections.emptyList(), pictureFrames));
     return new FlacStreamMetadata(
         minBlockSizeSamples,
         maxBlockSizeSamples,
@@ -317,10 +321,11 @@ public final class FlacStreamMetadata {
     }
   }
 
+  @Nullable
   private static Metadata buildMetadata(
       List<String> vorbisComments, List<PictureFrame> pictureFrames) {
     if (vorbisComments.isEmpty() && pictureFrames.isEmpty()) {
-      return new Metadata();
+      return null;
     }
 
     ArrayList<Metadata.Entry> metadataEntries = new ArrayList<>();
@@ -336,6 +341,6 @@ public final class FlacStreamMetadata {
     }
     metadataEntries.addAll(pictureFrames);
 
-    return metadataEntries.isEmpty() ? new Metadata() : new Metadata(metadataEntries);
+    return metadataEntries.isEmpty() ? null : new Metadata(metadataEntries);
   }
 }

library/core/src/test/assets/flac/bear.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/flac/bear_no_min_max_frame_size.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 9218FDB7
   total output bytes = 164431

library/core/src/test/assets/flac/bear_no_num_samples.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 49FA2C21
   total output bytes = 164431

library/core/src/test/assets/flac/bear_one_metadata_block.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/flac/bear_uncommon_sample_rate.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 7249A1B8
   total output bytes = 144086

library/core/src/test/assets/flac/bear_with_id3_disabled.flac.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/ogg/bear_flac.ogg.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/ogg/bear_flac.ogg.1.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 113666

library/core/src/test/assets/ogg/bear_flac.ogg.2.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 55652

library/core/src/test/assets/ogg/bear_flac.ogg.3.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 445

library/core/src/test/assets/ogg/bear_flac.ogg.unklen.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/ogg/bear_flac_noseektable.ogg.0.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/assets/ogg/bear_flac_noseektable.ogg.1.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 113666

library/core/src/test/assets/ogg/bear_flac_noseektable.ogg.2.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 55652

library/core/src/test/assets/ogg/bear_flac_noseektable.ogg.3.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 445

library/core/src/test/assets/ogg/bear_flac_noseektable.ogg.unklen.dump

@@ -24,7 +24,7 @@ track 0:
     selectionFlags = 0
     language = null
     drmInitData = -
-    metadata = entries=[]
+    metadata = null
     initializationData:
       data = length 42, hash 83F6895
   total output bytes = 164431

library/core/src/test/java/com/google/android/exoplayer2/util/FlacStreamMetadataTest.java

@@ -75,7 +75,7 @@ public final class FlacStreamMetadataTest {
                 /* pictureFrames= */ new ArrayList<>())
             .getMetadataCopyWithAppendedEntriesFrom(/* other= */ null);
 
-    assertThat(metadata.length()).isEqualTo(0);
+    assertThat(metadata).isNull();
   }
 
   @Test