Prioritize metadata seekers over index seeking in Mp3Extractor

The `FLAG_ENABLE_INDEX_SEEKING` flag now enables index seeking only as a fallback when no other seeking metadata (like Xing, VBRI, or MLLT) is present in the MP3 file. This ensures that more efficient metadata-based seekers are used when available.

Issue: #2839
PiperOrigin-RevId: 819419541

Author: rohitjoins

RELEASENOTES.md

@@ -147,6 +147,11 @@
         the whole file).
     *   Add support for extracting HEIC Motion Photos. The `HeifExtractor` can
         now parse HEIC files containing embedded video and audio tracks.
+    *   MP3: Change `FLAG_ENABLE_INDEX_SEEKING` to prefer seeking information
+        from metadata headers (like Xing and VBRI) when available, falling back
+        to index-based seeking if no other seeking information is present. This
+        improves performance for files with seeking metadata
+        ([#2839](https://github.com/androidx/media/issues/2839)).
 *   Inspector:
     *   Introduced a new `:media3-inspector` module to serve as the dedicated
         home for media inspection utilities. This module now houses a new

libraries/extractor/src/main/java/androidx/media3/extractor/mp3/Mp3Extractor.java

@@ -107,15 +107,17 @@ public final class Mp3Extractor implements Extractor {
   public static final int FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS = 1 << 1;
 
   /**
-   * Flag to force index seeking, in which a time-to-byte mapping is built as the file is read.
+   * Flag to enable index seeking, in which a time-to-byte mapping is built as the file is read. If
+   * other seeking metadata (e.g., Xing, VBRI, MLLT) is present in the file, it will be preferred
+   * for performance reasons. This flag allows index seeking to be used as a fallback in cases where
+   * no other seeking metadata is available.
    *
    * <p>This seeker may require to scan a significant portion of the file to compute a seek point.
    * Therefore, it should only be used if one of the following is true:
    *
    * <ul>
    *   <li>The file is small.
-   *   <li>The bitrate is variable (or it's unknown whether it's variable) and the file does not
-   *       provide precise enough seeking metadata.
+   *   <li>The bitrate is variable (or it's unknown whether it's variable).
    * </ul>
    */
   public static final int FLAG_ENABLE_INDEX_SEEKING = 1 << 2;
@@ -479,27 +481,23 @@ private Seeker computeSeeker(ExtractorInput input) throws IOException {
     }
 
     @Nullable Seeker resultSeeker = null;
-    if ((flags & FLAG_ENABLE_INDEX_SEEKING) != 0) {
-      long durationUs;
-      long dataEndPosition = C.INDEX_UNSET;
-      if (metadataSeeker != null) {
-        durationUs = metadataSeeker.getDurationUs();
-        dataEndPosition = metadataSeeker.getDataEndPosition();
-      } else if (seekFrameSeeker != null) {
-        durationUs = seekFrameSeeker.getDurationUs();
-        dataEndPosition = seekFrameSeeker.getDataEndPosition();
-      } else {
-        durationUs = getId3TlenUs(metadata);
-      }
-      resultSeeker =
-          new IndexSeeker(
-              durationUs, /* dataStartPosition= */ input.getPosition(), dataEndPosition);
-    } else if (metadataSeeker != null) {
+    if (metadataSeeker != null) {
       resultSeeker = metadataSeeker;
     } else if (seekFrameSeeker != null) {
       resultSeeker = seekFrameSeeker;
     }
 
+    if ((flags & FLAG_ENABLE_INDEX_SEEKING) != 0
+        && (resultSeeker == null || !resultSeeker.isSeekable())) {
+      long durationUs =
+          resultSeeker != null ? resultSeeker.getDurationUs() : getId3TlenUs(metadata);
+      long dataEndPosition =
+          resultSeeker != null ? resultSeeker.getDataEndPosition() : C.INDEX_UNSET;
+      resultSeeker =
+          new IndexSeeker(
+              durationUs, /* dataStartPosition= */ input.getPosition(), dataEndPosition);
+    }
+
     if (resultSeeker != null
         && shouldFallbackToConstantBitrateSeeking(resultSeeker)
         && resultSeeker.getDurationUs() != C.TIME_UNSET

libraries/extractor/src/test/java/androidx/media3/extractor/mp3/Mp3ExtractorTest.java

@@ -46,6 +46,15 @@ public void mp3SampleWithXingHeader() throws Exception {
         simulationConfig);
   }
 
+  @Test
+  public void mp3SampleWithXingHeader_indexSeekingFlag_usesXingSeeker() throws Exception {
+    ExtractorAsserts.assertBehavior(
+        () -> new Mp3Extractor(Mp3Extractor.FLAG_ENABLE_INDEX_SEEKING),
+        "media/mp3/bear-vbr-xing-header.mp3",
+        /* peekLimit= */ 1300,
+        simulationConfig);
+  }
+
   @Test
   public void mp3SampleWithXingHeader_noTableOfContents() throws Exception {
     ExtractorAsserts.assertBehavior(
@@ -55,6 +64,19 @@ public void mp3SampleWithXingHeader_noTableOfContents() throws Exception {
         simulationConfig);
   }
 
+  @Test
+  public void mp3SampleWithXingHeader_noTableOfContents_indexSeeking() throws Exception {
+    String filename = "mp3/bear-vbr-xing-header-no-toc.mp3";
+    ExtractorAsserts.assertBehavior(
+        () -> new Mp3Extractor(Mp3Extractor.FLAG_ENABLE_INDEX_SEEKING),
+        "media/" + filename,
+        /* peekLimit= */ 1300,
+        new AssertionConfig.Builder()
+            .setDumpFilesPrefix("extractordumps/" + filename + ".index-seeking")
+            .build(),
+        simulationConfig);
+  }
+
   @Test
   public void mp3SampleWithXingHeader_noTableOfContents_cbrSeeking() throws Exception {
     String filename = "mp3/bear-vbr-xing-header-no-toc.mp3";