Handle RTP timestamp wraparound in RtpReaderUtils

RTP timestamps are 32-bit unsigned integers. When calculating the time difference between two RTP timestamps, especially when one has wrapped around, a simple subtraction can yield a negative result. This change ensures that the difference is always treated as an unsigned value by masking the result of the subtraction with 0xFFFFFFFFL before scaling it to microseconds.

A test case is added to RtpH265ReaderTest to verify the correct handling of wrapped-around timestamps.

Issue: #2930
PiperOrigin-RevId: 848538759

Author: microkatz

RELEASENOTES.md

@@ -95,6 +95,8 @@
 *   DASH extension:
 *   Smooth Streaming extension:
 *   RTSP extension:
+    *   Correctly handle RTP Packets with timestamps that wrap around
+        ([#2930](https://github.com/androidx/media/issues/2930)).
 *   Decoder extensions (FFmpeg, VP9, AV1, etc.):
 *   MIDI extension:
 *   Leanback extension:

libraries/exoplayer_rtsp/src/main/java/androidx/media3/exoplayer/rtsp/reader/RtpReaderUtils.java

@@ -35,9 +35,12 @@ public static long toSampleTimeUs(
       long rtpTimestamp,
       long firstReceivedRtpTimestamp,
       int mediaFrequency) {
+    // Calculate the difference in RTP time, accounting for 32-bit unsigned wraparound.
+    // RTP timestamps are unsigned 32-bit integers.
+    long rtpTimestampDelta = (rtpTimestamp - firstReceivedRtpTimestamp) & 0xFFFFFFFFL;
     return startTimeOffsetUs
         + Util.scaleLargeTimestamp(
-            rtpTimestamp - firstReceivedRtpTimestamp,
+            rtpTimestampDelta,
             /* multiplier= */ C.MICROS_PER_SECOND,
             /* divisor= */ mediaFrequency);
   }

libraries/exoplayer_rtsp/src/test/java/androidx/media3/exoplayer/rtsp/reader/RtpReaderUtilsTest.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package androidx.media3.exoplayer.rtsp.reader;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit test for {@link RtpReaderUtils}. */
+@RunWith(AndroidJUnit4.class)
+public class RtpReaderUtilsTest {
+  @Test
+  public void toSampleTimeUs_withWrappedTimestamp_returnsCorrectSampleTimeUs() {
+    assertThat(
+            RtpReaderUtils.toSampleTimeUs(
+                /* startTimeOffsetUs= */ 0,
+                /* rtpTimestamp= */ 9_000_040L,
+                /* firstReceivedRtpTimestamp= */ 4_285_967_336L,
+                /* mediaFrequency= */ 90_000))
+        .isEqualTo(200_000_000L);
+  }
+}