add readSignedInt24 in ParsableByteArray

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

@@ -79,9 +79,7 @@ import com.google.android.exoplayer2.video.AvcConfig;
   @Override
   protected void parsePayload(ParsableByteArray data, long timeUs) throws ParserException {
     int packetType = data.readUnsignedByte();
-    int compositionTimeMs = data.readUnsignedInt24();
-    // compositionTimeMs is signed int 24, change unsigned int 24 to signed int 24
-    compositionTimeMs = (compositionTimeMs & 0x800000L) >>> 23 == 1 ? (compositionTimeMs | 0xff000000) : compositionTimeMs;
+    int compositionTimeMs = data.readSignedInt24();
 
     timeUs += compositionTimeMs * 1000L;
     // Parse avc sequence header in case this was not done before.

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

@@ -256,6 +256,14 @@ public final class ParsableByteArray {
         | (data[position++] & 0xFF);
   }
 
+  /**
+   * Reads the next three bytes as an signed value.
+   */
+  public int readSignedInt24() {
+    int ui24 = readUnsignedInt24();
+    return (ui24 & 0x800000L) >>> 23 == 1 ? (ui24 | 0xff000000) : ui24;
+  }
+
   /**
    * Reads the next three bytes as a signed value in little endian order.
    */

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

@@ -334,6 +334,22 @@ public final class ParsableByteArrayTest {
     assertThat(byteArray.getPosition()).isEqualTo(3);
   }
 
+  @Test
+  public void testReadPositiveSignedInt24() {
+    byte[] data = { 0x01, 0x02, (byte) 0xFF };
+    ParsableByteArray byteArray = new ParsableByteArray(data);
+    assertThat(byteArray.readSignedInt24()).isEqualTo(0x0102FF);
+    assertThat(byteArray.getPosition()).isEqualTo(3);
+  }
+
+  @Test
+  public void testReadNegativeSignedInt24() {
+    byte[] data = { (byte)0xFF, 0x02, (byte) 0x01 };
+    ParsableByteArray byteArray = new ParsableByteArray(data);
+    assertThat(byteArray.readSignedInt24()).isEqualTo(0xFFFF0201);
+    assertThat(byteArray.getPosition()).isEqualTo(3);
+  }
+
   @Test
   public void testReadLittleEndianUnsignedShort() {
     ParsableByteArray byteArray = new ParsableByteArray(new byte[] {