take byte offset into account when unsynchronizing an id3 frame

Issue #5673

PiperOrigin-RevId: 241328598

RELEASENOTES.md

@@ -90,7 +90,8 @@
 * Prevent seeking when ICY metadata is present to prevent playback problems
   ([#5658](https://github.com/google/ExoPlayer/issues/5658)).
 * Use full BCP 47 language tags in `Format`.
-* Select audio track based on system language if no preference is provided.
+* Take byte offset into account when unsynchronizing an id3 frame
+  ([#5673](https://github.com/google/ExoPlayer/issues/5673)).
 
 ### 2.9.6 ###
 

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

@@ -713,9 +713,11 @@ public final class Id3Decoder implements MetadataDecoder {
    */
   private static int removeUnsynchronization(ParsableByteArray data, int length) {
     byte[] bytes = data.data;
-    for (int i = data.getPosition(); i + 1 < length; i++) {
+    int startPosition = data.getPosition();
+    for (int i = startPosition; i + 1 < startPosition + length; i++) {
       if ((bytes[i] & 0xFF) == 0xFF && bytes[i + 1] == 0x00) {
-        System.arraycopy(bytes, i + 2, bytes, i + 1, length - i - 2);
+        int relativePosition = i - startPosition;
+        System.arraycopy(bytes, i + 2, bytes, i + 1, length - relativePosition - 2);
         length--;
       }
     }