Allow disabling ID3 metadata parsing if not required

Issue: #2553

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150184824

library/src/main/java/com/google/android/exoplayer2/extractor/GaplessInfoHolder.java

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.extractor;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.metadata.Metadata;
 import com.google.android.exoplayer2.metadata.id3.CommentFrame;
+import com.google.android.exoplayer2.metadata.id3.Id3Decoder.FramePredicate;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -26,6 +27,18 @@ import java.util.regex.Pattern;
  */
 public final class GaplessInfoHolder {
 
+  /**
+   * A {@link FramePredicate} suitable for use when decoding {@link Metadata} that will be passed
+   * to {@link #setFromMetadata(Metadata)}. Only frames that might contain gapless playback
+   * information are decoded.
+   */
+  public static final FramePredicate GAPLESS_INFO_ID3_FRAME_PREDICATE = new FramePredicate() {
+    @Override
+    public boolean evaluate(int majorVersion, int id0, int id1, int id2, int id3) {
+      return id0 == 'C' && id1 == 'O' && id2 == 'M' && (id3 == 'M' || majorVersion == 2);
+    }
+  };
+
   private static final String GAPLESS_COMMENT_ID = "iTunSMPB";
   private static final Pattern GAPLESS_COMMENT_PATTERN =
       Pattern.compile("^ [0-9a-fA-F]{8} ([0-9a-fA-F]{8}) ([0-9a-fA-F]{8})");

library/src/main/java/com/google/android/exoplayer2/extractor/mp3/Mp3Extractor.java

@@ -58,13 +58,18 @@ public final class Mp3Extractor implements Extractor {
    * Flags controlling the behavior of the extractor.
    */
   @Retention(RetentionPolicy.SOURCE)
-  @IntDef(flag = true, value = {FLAG_ENABLE_CONSTANT_BITRATE_SEEKING})
+  @IntDef(flag = true, value = {FLAG_ENABLE_CONSTANT_BITRATE_SEEKING, FLAG_DISABLE_ID3_METADATA})
   public @interface Flags {}
   /**
    * Flag to force enable seeking using a constant bitrate assumption in cases where seeking would
    * otherwise not be possible.
    */
   public static final int FLAG_ENABLE_CONSTANT_BITRATE_SEEKING = 1;
+  /**
+   * Flag to disable parsing of ID3 metadata. Can be set to save memory if ID3 metadata is not
+   * required.
+   */
+  public static final int FLAG_DISABLE_ID3_METADATA = 2;
 
   /**
    * The maximum number of bytes to search when synchronizing, before giving up.
@@ -178,7 +183,8 @@ public final class Mp3Extractor implements Extractor {
       trackOutput.format(Format.createAudioSampleFormat(null, synchronizedHeader.mimeType, null,
           Format.NO_VALUE, MpegAudioHeader.MAX_FRAME_SIZE_BYTES, synchronizedHeader.channels,
           synchronizedHeader.sampleRate, Format.NO_VALUE, gaplessInfoHolder.encoderDelay,
-          gaplessInfoHolder.encoderPadding, null, null, 0, null, metadata));
+          gaplessInfoHolder.encoderPadding, null, null, 0, null,
+          (flags & FLAG_DISABLE_ID3_METADATA) != 0 ? null : metadata));
     }
     return readSample(input);
   }
@@ -311,7 +317,11 @@ public final class Mp3Extractor implements Extractor {
         byte[] id3Data = new byte[tagLength];
         System.arraycopy(scratch.data, 0, id3Data, 0, Id3Decoder.ID3_HEADER_LENGTH);
         input.peekFully(id3Data, Id3Decoder.ID3_HEADER_LENGTH, framesLength);
-        metadata = new Id3Decoder().decode(id3Data, tagLength);
+        // We need to parse enough ID3 metadata to retrieve any gapless playback information even
+        // if ID3 metadata parsing is disabled.
+        Id3Decoder.FramePredicate id3FramePredicate = (flags & FLAG_DISABLE_ID3_METADATA) != 0
+            ? GaplessInfoHolder.GAPLESS_INFO_ID3_FRAME_PREDICATE : null;
+        metadata = new Id3Decoder(id3FramePredicate).decode(id3Data, tagLength);
         if (metadata != null) {
           gaplessInfoHolder.setFromMetadata(metadata);
         }

library/src/main/java/com/google/android/exoplayer2/metadata/id3/Id3Decoder.java

@@ -34,6 +34,25 @@ import java.util.Locale;
  */
 public final class Id3Decoder implements MetadataDecoder {
 
+  /**
+   * A predicate for determining whether individual frames should be decoded.
+   */
+  public interface FramePredicate {
+
+    /**
+     * Returns whether a frame with the specified parameters should be decoded.
+     *
+     * @param majorVersion The major version of the ID3 tag.
+     * @param id0 The first byte of the frame ID.
+     * @param id1 The second byte of the frame ID.
+     * @param id2 The third byte of the frame ID.
+     * @param id3 The fourth byte of the frame ID.
+     * @return Whether the frame should be decoded.
+     */
+    boolean evaluate(int majorVersion, int id0, int id1, int id2, int id3);
+
+  }
+
   private static final String TAG = "Id3Decoder";
 
   /**
@@ -50,6 +69,19 @@ public final class Id3Decoder implements MetadataDecoder {
   private static final int ID3_TEXT_ENCODING_UTF_16BE = 2;
   private static final int ID3_TEXT_ENCODING_UTF_8 = 3;
 
+  private final FramePredicate framePredicate;
+
+  public Id3Decoder() {
+    this(null);
+  }
+
+  /**
+   * @param framePredicate Determines which frames are decoded. May be null to decode all frames.
+   */
+  public Id3Decoder(FramePredicate framePredicate) {
+    this.framePredicate = framePredicate;
+  }
+
   @Override
   public Metadata decode(MetadataInputBuffer inputBuffer) {
     ByteBuffer buffer = inputBuffer.data;
@@ -94,7 +126,7 @@ public final class Id3Decoder implements MetadataDecoder {
     int frameHeaderSize = id3Header.majorVersion == 2 ? 6 : 10;
     while (id3Data.bytesLeft() >= frameHeaderSize) {
       Id3Frame frame = decodeFrame(id3Header.majorVersion, id3Data, unsignedIntFrameSizeHack,
-          frameHeaderSize);
+          frameHeaderSize, framePredicate);
       if (frame != null) {
         id3Frames.add(frame);
       }
@@ -200,7 +232,7 @@ public final class Id3Decoder implements MetadataDecoder {
   }
 
   private static Id3Frame decodeFrame(int majorVersion, ParsableByteArray id3Data,
-      boolean unsignedIntFrameSizeHack, int frameHeaderSize) {
+      boolean unsignedIntFrameSizeHack, int frameHeaderSize, FramePredicate framePredicate) {
     int frameId0 = id3Data.readUnsignedByte();
     int frameId1 = id3Data.readUnsignedByte();
     int frameId2 = id3Data.readUnsignedByte();
@@ -234,6 +266,13 @@ public final class Id3Decoder implements MetadataDecoder {
       return null;
     }
 
+    if (framePredicate != null
+        && !framePredicate.evaluate(majorVersion, frameId0, frameId1, frameId2, frameId3)) {
+      // Filtered by the predicate.
+      id3Data.setPosition(nextFramePosition);
+      return null;
+    }
+
     // Frame flags.
     boolean isCompressed = false;
     boolean isEncrypted = false;
@@ -302,10 +341,10 @@ public final class Id3Decoder implements MetadataDecoder {
         frame = decodeCommentFrame(id3Data, frameSize);
       } else if (frameId0 == 'C' && frameId1 == 'H' && frameId2 == 'A' && frameId3 == 'P') {
         frame = decodeChapterFrame(id3Data, frameSize, majorVersion, unsignedIntFrameSizeHack,
-            frameHeaderSize);
+            frameHeaderSize, framePredicate);
       } else if (frameId0 == 'C' && frameId1 == 'T' && frameId2 == 'O' && frameId3 == 'C') {
         frame = decodeChapterTOCFrame(id3Data, frameSize, majorVersion, unsignedIntFrameSizeHack,
-            frameHeaderSize);
+            frameHeaderSize, framePredicate);
       } else {
         String id = majorVersion == 2
             ? String.format(Locale.US, "%c%c%c", frameId0, frameId1, frameId2)
@@ -513,8 +552,8 @@ public final class Id3Decoder implements MetadataDecoder {
   }
 
   private static ChapterFrame decodeChapterFrame(ParsableByteArray id3Data, int frameSize,
-      int majorVersion, boolean unsignedIntFrameSizeHack, int frameHeaderSize)
-      throws UnsupportedEncodingException {
+      int majorVersion, boolean unsignedIntFrameSizeHack, int frameHeaderSize,
+      FramePredicate framePredicate) throws UnsupportedEncodingException {
     int framePosition = id3Data.getPosition();
     int chapterIdEndIndex = indexOfZeroByte(id3Data.data, framePosition);
     String chapterId = new String(id3Data.data, framePosition, chapterIdEndIndex - framePosition,
@@ -536,7 +575,7 @@ public final class Id3Decoder implements MetadataDecoder {
     int limit = framePosition + frameSize;
     while (id3Data.getPosition() < limit) {
       Id3Frame frame = decodeFrame(majorVersion, id3Data, unsignedIntFrameSizeHack,
-          frameHeaderSize);
+          frameHeaderSize, framePredicate);
       if (frame != null) {
         subFrames.add(frame);
       }
@@ -548,8 +587,8 @@ public final class Id3Decoder implements MetadataDecoder {
   }
 
   private static ChapterTocFrame decodeChapterTOCFrame(ParsableByteArray id3Data, int frameSize,
-      int majorVersion, boolean unsignedIntFrameSizeHack, int frameHeaderSize)
-      throws UnsupportedEncodingException {
+      int majorVersion, boolean unsignedIntFrameSizeHack, int frameHeaderSize,
+      FramePredicate framePredicate) throws UnsupportedEncodingException {
     int framePosition = id3Data.getPosition();
     int elementIdEndIndex = indexOfZeroByte(id3Data.data, framePosition);
     String elementId = new String(id3Data.data, framePosition, elementIdEndIndex - framePosition,
@@ -573,7 +612,7 @@ public final class Id3Decoder implements MetadataDecoder {
     int limit = framePosition + frameSize;
     while (id3Data.getPosition() < limit) {
       Id3Frame frame = decodeFrame(majorVersion, id3Data, unsignedIntFrameSizeHack,
-          frameHeaderSize);
+          frameHeaderSize, framePredicate);
       if (frame != null) {
         subFrames.add(frame);
       }