ID3: Fix end-of-string detection for UTF-16

The current detection logic checks that the two byte terminator starts
at an even position in the ID3 data, where-as it should check that it
starts at an even position relative to the start of the string.

Issue: #9087
PiperOrigin-RevId: 395274934

RELEASENOTES.md

@@ -12,6 +12,8 @@
 *   Extractors:
     *   Support TS packets without PTS flag
         ([#9294](https://github.com/google/ExoPlayer/issues/9294)).
+    *   ID3: Fix issue decoding ID3 tags containing UTF-16 encoded strings
+        ([#9087](https://github.com/google/ExoPlayer/issues/9087)).
 *   Video:
     *   Request smaller decoder input buffers for Dolby Vision. This fixes an
         issue that could cause UHD Dolby Vision playbacks to fail on some

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

@@ -806,9 +806,9 @@ public final class Id3Decoder extends SimpleMetadataDecoder {
       return terminationPos;
     }
 
-    // Otherwise ensure an even index and look for a second zero byte.
+    // Otherwise ensure an even offset from the start, and look for a second zero byte.
     while (terminationPos < data.length - 1) {
-      if (terminationPos % 2 == 0 && data[terminationPos + 1] == (byte) 0) {
+      if ((terminationPos - fromIndex) % 2 == 0 && data[terminationPos + 1] == (byte) 0) {
         return terminationPos;
       }
       terminationPos = indexOfZeroByte(data, terminationPos + 1);

library/common/src/test/java/com/google/android/exoplayer2/metadata/id3/Id3DecoderTest.java

@@ -38,6 +38,7 @@ public final class Id3DecoderTest {
 
   @Test
   public void decodeTxxxFrame() {
+    // Test UTF-8.
     byte[] rawId3 =
         buildSingleFrameTag(
             "TXXX",
@@ -53,6 +54,21 @@ public final class Id3DecoderTest {
     assertThat(textInformationFrame.description).isEmpty();
     assertThat(textInformationFrame.value).isEqualTo("mdialog_VINDICO1527664_start");
 
+    // Test UTF-16.
+    rawId3 =
+        buildSingleFrameTag(
+            "TXXX",
+            new byte[] {
+              1, 0, 72, 0, 101, 0, 108, 0, 108, 0, 111, 0, 32, 0, 87, 0, 111, 0, 114, 0, 108, 0,
+              100, 0, 0
+            });
+    metadata = decoder.decode(rawId3, rawId3.length);
+    assertThat(metadata.length()).isEqualTo(1);
+    textInformationFrame = (TextInformationFrame) metadata.get(0);
+    assertThat(textInformationFrame.id).isEqualTo("TXXX");
+    assertThat(textInformationFrame.description).isEqualTo("Hello World");
+    assertThat(textInformationFrame.value).isEmpty();
+
     // Test empty.
     rawId3 = buildSingleFrameTag("TXXX", new byte[0]);
     metadata = decoder.decode(rawId3, rawId3.length);
@@ -220,6 +236,43 @@ public final class Id3DecoderTest {
     assertThat(apicFrame.description).isEqualTo("Hello World");
     assertThat(apicFrame.pictureData).hasLength(10);
     assertThat(apicFrame.pictureData).isEqualTo(new byte[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 0});
+
+    // Test with UTF-16 description at even offset.
+    rawId3 =
+        buildSingleFrameTag(
+            "APIC",
+            new byte[] {
+              1, 105, 109, 97, 103, 101, 47, 106, 112, 101, 103, 0, 16, 0, 72, 0, 101, 0, 108, 0,
+              108, 0, 111, 0, 32, 0, 87, 0, 111, 0, 114, 0, 108, 0, 100, 0, 0, 1, 2, 3, 4, 5, 6, 7,
+              8, 9, 0
+            });
+    decoder = new Id3Decoder();
+    metadata = decoder.decode(rawId3, rawId3.length);
+    assertThat(metadata.length()).isEqualTo(1);
+    apicFrame = (ApicFrame) metadata.get(0);
+    assertThat(apicFrame.mimeType).isEqualTo("image/jpeg");
+    assertThat(apicFrame.pictureType).isEqualTo(16);
+    assertThat(apicFrame.description).isEqualTo("Hello World");
+    assertThat(apicFrame.pictureData).hasLength(10);
+    assertThat(apicFrame.pictureData).isEqualTo(new byte[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 0});
+
+    // Test with UTF-16 description at odd offset.
+    rawId3 =
+        buildSingleFrameTag(
+            "APIC",
+            new byte[] {
+              1, 105, 109, 97, 103, 101, 47, 112, 110, 103, 0, 16, 0, 72, 0, 101, 0, 108, 0, 108, 0,
+              111, 0, 32, 0, 87, 0, 111, 0, 114, 0, 108, 0, 100, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0
+            });
+    decoder = new Id3Decoder();
+    metadata = decoder.decode(rawId3, rawId3.length);
+    assertThat(metadata.length()).isEqualTo(1);
+    apicFrame = (ApicFrame) metadata.get(0);
+    assertThat(apicFrame.mimeType).isEqualTo("image/png");
+    assertThat(apicFrame.pictureType).isEqualTo(16);
+    assertThat(apicFrame.description).isEqualTo("Hello World");
+    assertThat(apicFrame.pictureData).hasLength(10);
+    assertThat(apicFrame.pictureData).isEqualTo(new byte[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 0});
   }
 
   @Test