diff --git a/library/core/src/main/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessor.java b/library/core/src/main/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessor.java
index 8d84325d93..f630c267e6 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessor.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessor.java
@@ -155,18 +155,20 @@ import java.nio.ByteBuffer;
   @Override
   protected void onFlush() {
     if (reconfigurationPending) {
-      // This is the initial flush after reconfiguration. Prepare to trim bytes from the start/end.
+      // Flushing activates the new configuration, so prepare to trim bytes from the start/end.
       reconfigurationPending = false;
       endBuffer = new byte[trimEndFrames * inputAudioFormat.bytesPerFrame];
       pendingTrimStartBytes = trimStartFrames * inputAudioFormat.bytesPerFrame;
-    } else {
-      // This is a flush during playback (after the initial flush). We assume this was caused by a
-      // seek to a non-zero position and clear pending start bytes. This assumption may be wrong (we
-      // may be seeking to zero), but playing data that should have been trimmed shouldn't be
-      // noticeable after a seek. Ideally we would check the timestamp of the first input buffer
-      // queued after flushing to decide whether to trim (see also [Internal: b/77292509]).
-      pendingTrimStartBytes = 0;
     }
+
+    // TODO(internal b/77292509): Flushing occurs to activate a configuration (handled above) but
+    // also when seeking within a stream. This implementation currently doesn't handle seek to start
+    // (where we need to trim at the start again), nor seeks to non-zero positions before start
+    // trimming has occurred (where we should set pendingTrimStartBytes to zero). These cases can be
+    // fixed by trimming in queueInput based on timestamp, once that information is available.
+
+    // Any data in the end buffer should no longer be output if we are playing from a different
+    // position, so discard it and refill the buffer using new input.
     endBufferSize = 0;
   }
 
diff --git a/library/core/src/test/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessorTest.java b/library/core/src/test/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessorTest.java
new file mode 100644
index 0000000000..19a1ad19c3
--- /dev/null
+++ b/library/core/src/test/java/com/google/android/exoplayer2/audio/TrimmingAudioProcessorTest.java
@@ -0,0 +1,101 @@
+/*
+ * Copyright 2020 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 com.google.android.exoplayer2.audio;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.audio.AudioProcessor.AudioFormat;
+import java.nio.ByteBuffer;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link TrimmingAudioProcessor}. */
+@RunWith(AndroidJUnit4.class)
+public final class TrimmingAudioProcessorTest {
+
+  private static final AudioFormat AUDIO_FORMAT =
+      new AudioFormat(/* sampleRate= */ 44100, /* channelCount= */ 2, C.ENCODING_PCM_16BIT);
+  private static final int TRACK_ONE_UNTRIMMED_FRAME_COUNT = 1024;
+  private static final int TRACK_ONE_TRIM_START_FRAME_COUNT = 64;
+  private static final int TRACK_ONE_TRIM_END_FRAME_COUNT = 32;
+  private static final int TRACK_TWO_TRIM_START_FRAME_COUNT = 128;
+  private static final int TRACK_TWO_TRIM_END_FRAME_COUNT = 16;
+
+  private static final int TRACK_ONE_BUFFER_SIZE_BYTES =
+      AUDIO_FORMAT.bytesPerFrame * TRACK_ONE_UNTRIMMED_FRAME_COUNT;
+  private static final int TRACK_ONE_TRIMMED_BUFFER_SIZE_BYTES =
+      TRACK_ONE_BUFFER_SIZE_BYTES
+          - AUDIO_FORMAT.bytesPerFrame
+              * (TRACK_ONE_TRIM_START_FRAME_COUNT + TRACK_ONE_TRIM_END_FRAME_COUNT);
+
+  private TrimmingAudioProcessor trimmingAudioProcessor;
+
+  @Before
+  public void setUp() {
+    trimmingAudioProcessor = new TrimmingAudioProcessor();
+  }
+
+  @After
+  public void tearDown() {
+    trimmingAudioProcessor.reset();
+  }
+
+  @Test
+  public void flushTwice_trimsStartAndEnd() throws Exception {
+    trimmingAudioProcessor.setTrimFrameCount(
+        TRACK_ONE_TRIM_START_FRAME_COUNT, TRACK_ONE_TRIM_END_FRAME_COUNT);
+    trimmingAudioProcessor.configure(AUDIO_FORMAT);
+    trimmingAudioProcessor.flush();
+    trimmingAudioProcessor.flush();
+
+    int outputSizeBytes = feedAndDrainAudioProcessorToEndOfTrackOne();
+
+    assertThat(trimmingAudioProcessor.getTrimmedFrameCount())
+        .isEqualTo(TRACK_ONE_TRIM_START_FRAME_COUNT + TRACK_ONE_TRIM_END_FRAME_COUNT);
+    assertThat(outputSizeBytes).isEqualTo(TRACK_ONE_TRIMMED_BUFFER_SIZE_BYTES);
+  }
+
+  /**
+   * Feeds and drains the audio processor up to the end of track one, returning the total output
+   * size in bytes.
+   */
+  private int feedAndDrainAudioProcessorToEndOfTrackOne() throws Exception {
+    // Feed and drain the processor, simulating a gapless transition to another track.
+    ByteBuffer inputBuffer = ByteBuffer.allocate(TRACK_ONE_BUFFER_SIZE_BYTES);
+    int outputSize = 0;
+    while (!trimmingAudioProcessor.isEnded()) {
+      if (inputBuffer.hasRemaining()) {
+        trimmingAudioProcessor.queueInput(inputBuffer);
+        if (!inputBuffer.hasRemaining()) {
+          // Reconfigure for a next track then begin draining.
+          trimmingAudioProcessor.setTrimFrameCount(
+              TRACK_TWO_TRIM_START_FRAME_COUNT, TRACK_TWO_TRIM_END_FRAME_COUNT);
+          trimmingAudioProcessor.configure(AUDIO_FORMAT);
+          trimmingAudioProcessor.queueEndOfStream();
+        }
+      }
+      ByteBuffer outputBuffer = trimmingAudioProcessor.getOutput();
+      outputSize += outputBuffer.remaining();
+      outputBuffer.clear();
+    }
+    trimmingAudioProcessor.reset();
+    return outputSize;
+  }
+}