Add forceVideoTrack flag on EditedMediaItemSequence

This is similar to forceAudioTrack.

PiperOrigin-RevId: 743235372

libraries/common/src/main/java/androidx/media3/common/util/ConditionVariable.java

@@ -82,6 +82,7 @@ public class ConditionVariable {
    */
   public synchronized void block() throws InterruptedException {
     while (!isOpen) {
+      clock.onThreadBlocked();
       wait();
     }
   }
@@ -105,6 +106,7 @@ public class ConditionVariable {
       block();
     } else {
       while (!isOpen && nowMs < endMs) {
+        clock.onThreadBlocked();
         wait(endMs - nowMs);
         nowMs = clock.elapsedRealtime();
       }
@@ -113,14 +115,17 @@ public class ConditionVariable {
   }
 
   /**
-   * Blocks until the condition is open. Unlike {@link #block}, this method will continue to block
-   * if the calling thread is interrupted. If the calling thread was interrupted then its {@link
-   * Thread#isInterrupted() interrupted status} will be set when the method returns.
+   * Blocks until the condition is open.
+   *
+   * <p>Unlike {@link #block}, this method will continue to block if the calling thread is
+   * interrupted. If the calling thread was interrupted then its {@link Thread#isInterrupted()
+   * interrupted status} will be set when the method returns.
    */
   public synchronized void blockUninterruptible() {
     boolean wasInterrupted = false;
     while (!isOpen) {
       try {
+        clock.onThreadBlocked();
         wait();
       } catch (InterruptedException e) {
         wasInterrupted = true;
@@ -132,6 +137,45 @@ public class ConditionVariable {
     }
   }
 
+  /**
+   * Blocks until the condition is open or until {@code timeoutMs} have passed.
+   *
+   * <p>Unlike {@link #block}, this method will continue to block if the calling thread is
+   * interrupted. If the calling thread was interrupted then its {@link Thread#isInterrupted()
+   * interrupted status} will be set when the method returns.
+   *
+   * @param timeoutMs The maximum time to wait in milliseconds. If {@code timeoutMs <= 0} then the
+   *     call will return immediately without blocking.
+   * @return True if the condition was opened, false if the call returns because of the timeout.
+   */
+  public synchronized boolean blockUninterruptible(long timeoutMs) {
+    if (timeoutMs <= 0) {
+      return isOpen;
+    }
+    long nowMs = clock.elapsedRealtime();
+    long endMs = nowMs + timeoutMs;
+    if (endMs < nowMs) {
+      // timeoutMs is large enough for (nowMs + timeoutMs) to rollover. Block indefinitely.
+      blockUninterruptible();
+    } else {
+      boolean wasInterrupted = false;
+      while (!isOpen && nowMs < endMs) {
+        try {
+          clock.onThreadBlocked();
+          wait(endMs - nowMs);
+        } catch (InterruptedException e) {
+          wasInterrupted = true;
+        }
+        nowMs = clock.elapsedRealtime();
+      }
+      if (wasInterrupted) {
+        // Restore the interrupted status.
+        Thread.currentThread().interrupt();
+      }
+    }
+    return isOpen;
+  }
+
   /** Returns whether the condition is opened. */
   public synchronized boolean isOpen() {
     return isOpen;

libraries/common/src/test/java/androidx/media3/common/util/ConditionVariableTest.java

@@ -33,14 +33,14 @@ public class ConditionVariableTest {
   }
 
   @Test
-  public void blockWithTimeout_timesOut() throws InterruptedException {
+  public void block_withTimeoutUnopened_timesOut() throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
     assertThat(conditionVariable.block(1)).isFalse();
     assertThat(conditionVariable.isOpen()).isFalse();
   }
 
   @Test
-  public void blockWithTimeout_blocksForAtLeastTimeout() throws InterruptedException {
+  public void block_withTimeoutUnopened_blocksForAtLeastTimeout() throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
     long startTimeMs = System.currentTimeMillis();
     assertThat(conditionVariable.block(/* timeoutMs= */ 500)).isFalse();
@@ -49,7 +49,8 @@ public class ConditionVariableTest {
   }
 
   @Test
-  public void blockWithMaxTimeout_blocks_thenThrowsWhenInterrupted() throws InterruptedException {
+  public void block_withMaxTimeoutUnopened_blocksThenThrowsWhenInterrupted()
+      throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
 
     AtomicBoolean blockReturned = new AtomicBoolean();
@@ -76,7 +77,7 @@ public class ConditionVariableTest {
   }
 
   @Test
-  public void block_blocks_thenThrowsWhenInterrupted() throws InterruptedException {
+  public void block_unopened_blocksThenThrowsWhenInterrupted() throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
 
     AtomicBoolean blockReturned = new AtomicBoolean();
@@ -103,7 +104,7 @@ public class ConditionVariableTest {
   }
 
   @Test
-  public void block_blocks_thenReturnsWhenOpened() throws InterruptedException {
+  public void block_opened_blocksThenReturnsWhenOpened() throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
 
     AtomicBoolean blockReturned = new AtomicBoolean();
@@ -130,7 +131,7 @@ public class ConditionVariableTest {
   }
 
   @Test
-  public void blockUnterruptible_blocksIfInterrupted_thenUnblocksWhenOpened()
+  public void blockUninterruptible_blocksIfInterruptedThenUnblocksWhenOpened()
       throws InterruptedException {
     ConditionVariable conditionVariable = buildTestConditionVariable();
 
@@ -140,8 +141,8 @@ public class ConditionVariableTest {
         new Thread(
             () -> {
               conditionVariable.blockUninterruptible();
-              blockReturned.set(true);
               interruptedStatusSet.set(Thread.currentThread().isInterrupted());
+              blockReturned.set(true);
             });
 
     blockingThread.start();
@@ -160,6 +161,58 @@ public class ConditionVariableTest {
     assertThat(conditionVariable.isOpen()).isTrue();
   }
 
+  @Test
+  public void blockUninterruptible_withTimeoutUnopened_timesOut() throws InterruptedException {
+    ConditionVariable conditionVariable = buildTestConditionVariable();
+
+    assertThat(conditionVariable.blockUninterruptible(1)).isFalse();
+    assertThat(conditionVariable.isOpen()).isFalse();
+  }
+
+  @Test
+  public void blockUninterruptible_withTimeoutUnopened_blocksForAtLeastTimeout()
+      throws InterruptedException {
+    ConditionVariable conditionVariable = buildTestConditionVariable();
+
+    long startTimeMs = System.currentTimeMillis();
+    assertThat(conditionVariable.blockUninterruptible(/* timeoutMs= */ 500)).isFalse();
+    long endTimeMs = System.currentTimeMillis();
+
+    assertThat(endTimeMs - startTimeMs).isAtLeast(500);
+  }
+
+  @Test
+  public void blockUninterruptible_withMaxTimeout_blocksUntilOpened() throws InterruptedException {
+    ConditionVariable conditionVariable = buildTestConditionVariable();
+    AtomicBoolean blockReturned = new AtomicBoolean();
+    AtomicBoolean interruptedStatusSet = new AtomicBoolean();
+    Thread blockingThread =
+        new Thread(
+            () -> {
+              conditionVariable.blockUninterruptible(/* timeoutMs= */ Long.MAX_VALUE);
+              interruptedStatusSet.set(Thread.currentThread().isInterrupted());
+              blockReturned.set(true);
+            });
+
+    blockingThread.start();
+    Thread.sleep(500);
+
+    assertThat(blockReturned.get()).isFalse();
+
+    blockingThread.interrupt();
+    Thread.sleep(500);
+
+    // blockUninterruptible should still be blocked.
+    assertThat(blockReturned.get()).isFalse();
+
+    conditionVariable.open();
+    blockingThread.join();
+
+    // blockUninterruptible should have set the thread's interrupted status on exit.
+    assertThat(interruptedStatusSet.get()).isTrue();
+    assertThat(conditionVariable.isOpen()).isTrue();
+  }
+
   private static ConditionVariable buildTestConditionVariable() {
     return new ConditionVariable(
         new SystemClock() {

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/ExoPlayerImplInternal.java

@@ -54,6 +54,7 @@ import androidx.media3.common.Player.RepeatMode;
 import androidx.media3.common.Timeline;
 import androidx.media3.common.util.Assertions;
 import androidx.media3.common.util.Clock;
+import androidx.media3.common.util.ConditionVariable;
 import androidx.media3.common.util.HandlerWrapper;
 import androidx.media3.common.util.Log;
 import androidx.media3.common.util.TraceUtil;
@@ -80,7 +81,6 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 /** Implements the internal behavior of {@link ExoPlayerImpl}. */
 /* package */ final class ExoPlayerImplInternal
@@ -536,12 +536,11 @@ import java.util.concurrent.atomic.AtomicBoolean;
       handler.obtainMessage(MSG_SET_FOREGROUND_MODE, /* foregroundMode */ 1, 0).sendToTarget();
       return true;
     } else {
-      AtomicBoolean processedFlag = new AtomicBoolean();
+      ConditionVariable processedCondition = new ConditionVariable(clock);
       handler
-          .obtainMessage(MSG_SET_FOREGROUND_MODE, /* foregroundMode */ 0, 0, processedFlag)
+          .obtainMessage(MSG_SET_FOREGROUND_MODE, /* foregroundMode */ 0, 0, processedCondition)
           .sendToTarget();
-      waitUninterruptibly(processedFlag, setForegroundModeTimeoutMs);
-      return processedFlag.get();
+      return processedCondition.blockUninterruptible(setForegroundModeTimeoutMs);
     }
   }
 
@@ -560,13 +559,12 @@ import java.util.concurrent.atomic.AtomicBoolean;
     if (releasedOnApplicationThread || !playbackLooper.getThread().isAlive()) {
       return true;
     }
-    AtomicBoolean processedFlag = new AtomicBoolean();
+    ConditionVariable processedCondition = new ConditionVariable(clock);
     handler
-        .obtainMessage(MSG_SET_VIDEO_OUTPUT, new Pair<>(videoOutput, processedFlag))
+        .obtainMessage(MSG_SET_VIDEO_OUTPUT, new Pair<>(videoOutput, processedCondition))
         .sendToTarget();
     if (timeoutMs != C.TIME_UNSET) {
-      waitUninterruptibly(processedFlag, timeoutMs);
-      return processedFlag.get();
+      return processedCondition.blockUninterruptible(timeoutMs);
     }
     return true;
   }
@@ -581,10 +579,9 @@ import java.util.concurrent.atomic.AtomicBoolean;
       return true;
     }
     releasedOnApplicationThread = true;
-    AtomicBoolean processedFlag = new AtomicBoolean();
-    handler.obtainMessage(MSG_RELEASE, processedFlag).sendToTarget();
-    waitUninterruptibly(processedFlag, releaseTimeoutMs);
-    return processedFlag.get();
+    ConditionVariable processedCondition = new ConditionVariable(clock);
+    handler.obtainMessage(MSG_RELEASE, processedCondition).sendToTarget();
+    return processedCondition.blockUninterruptible(releaseTimeoutMs);
   }
 
   public Looper getPlaybackLooper() {
@@ -707,13 +704,15 @@ import java.util.concurrent.atomic.AtomicBoolean;
           break;
         case MSG_SET_FOREGROUND_MODE:
           setForegroundModeInternal(
-              /* foregroundMode= */ msg.arg1 != 0, /* processedFlag= */ (AtomicBoolean) msg.obj);
+              /* foregroundMode= */ msg.arg1 != 0,
+              /* processedCondition= */ (ConditionVariable) msg.obj);
           break;
         case MSG_SET_VIDEO_OUTPUT:
-          Pair<Object, AtomicBoolean> setVideoOutputPayload = (Pair<Object, AtomicBoolean>) msg.obj;
+          Pair<Object, ConditionVariable> setVideoOutputPayload =
+              (Pair<Object, ConditionVariable>) msg.obj;
           setVideoOutputInternal(
               /* videoOutput= */ setVideoOutputPayload.first,
-              /* processedFlag= */ setVideoOutputPayload.second);
+              /* processedCondition= */ setVideoOutputPayload.second);
           break;
         case MSG_STOP:
           stopInternal(/* forceResetRenderers= */ false, /* acknowledgeStop= */ true);
@@ -783,7 +782,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
           setVideoFrameMetadataListenerInternal((VideoFrameMetadataListener) msg.obj);
           break;
         case MSG_RELEASE:
-          releaseInternal(/* processedFlag= */ (AtomicBoolean) msg.obj);
+          releaseInternal(/* processedCondition= */ (ConditionVariable) msg.obj);
           // Return immediately to not send playback info updates after release.
           return true;
         default:
@@ -916,36 +915,6 @@ import java.util.concurrent.atomic.AtomicBoolean;
     playbackInfo = playbackInfo.copyWithPlaybackError(error);
   }
 
-  /**
-   * Blocks the current thread until a condition becomes true or the specified amount of time has
-   * elapsed.
-   *
-   * <p>If the current thread is interrupted while waiting for the condition to become true, this
-   * method will restore the interrupt <b>after</b> the condition became true or the operation times
-   * out.
-   *
-   * @param condition The condition.
-   * @param timeoutMs The time in milliseconds to wait for the condition to become true.
-   */
-  private synchronized void waitUninterruptibly(AtomicBoolean condition, long timeoutMs) {
-    long deadlineMs = clock.elapsedRealtime() + timeoutMs;
-    long remainingMs = timeoutMs;
-    boolean wasInterrupted = false;
-    while (!condition.get() && remainingMs > 0) {
-      try {
-        clock.onThreadBlocked();
-        wait(remainingMs);
-      } catch (InterruptedException e) {
-        wasInterrupted = true;
-      }
-      remainingMs = deadlineMs - clock.elapsedRealtime();
-    }
-    if (wasInterrupted) {
-      // Restore the interrupted status.
-      Thread.currentThread().interrupt();
-    }
-  }
-
   private void setState(int state) {
     if (playbackInfo.playbackState != state) {
       if (state != Player.STATE_BUFFERING) {
@@ -1776,7 +1745,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
   }
 
   private void setForegroundModeInternal(
-      boolean foregroundMode, @Nullable AtomicBoolean processedFlag) {
+      boolean foregroundMode, @Nullable ConditionVariable processedCondition) {
     if (this.foregroundMode != foregroundMode) {
       this.foregroundMode = foregroundMode;
       if (!foregroundMode) {
@@ -1785,16 +1754,13 @@ import java.util.concurrent.atomic.AtomicBoolean;
         }
       }
     }
-    if (processedFlag != null) {
-      synchronized (this) {
-        processedFlag.set(true);
-        notifyAll();
-      }
+    if (processedCondition != null) {
+      processedCondition.open();
     }
   }
 
   private void setVideoOutputInternal(
-      @Nullable Object videoOutput, @Nullable AtomicBoolean processedFlag)
+      @Nullable Object videoOutput, @Nullable ConditionVariable processedCondition)
       throws ExoPlaybackException {
     for (RendererHolder renderer : renderers) {
       renderer.setVideoOutput(videoOutput);
@@ -1803,11 +1769,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
         || playbackInfo.playbackState == Player.STATE_BUFFERING) {
       handler.sendEmptyMessage(MSG_DO_SOME_WORK);
     }
-    if (processedFlag != null) {
-      synchronized (this) {
-        processedFlag.set(true);
-        notifyAll();
-      }
+    if (processedCondition != null) {
+      processedCondition.open();
     }
   }
 
@@ -1823,7 +1786,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
     setState(Player.STATE_IDLE);
   }
 
-  private void releaseInternal(AtomicBoolean processedFlag) {
+  private void releaseInternal(ConditionVariable processedCondition) {
     try {
       resetInternal(
           /* resetRenderers= */ true,
@@ -1837,10 +1800,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
       setState(Player.STATE_IDLE);
     } finally {
       playbackLooperProvider.releaseLooper();
-      synchronized (this) {
-        processedFlag.set(true);
-        notifyAll();
-      }
+      processedCondition.open();
     }
   }
 

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/e2etest/ExternallyLoadedImagePlaybackTest.java

@@ -161,7 +161,8 @@ public final class ExternallyLoadedImagePlaybackTest {
     MediaSource.Factory mediaSourceFactory =
         new DefaultMediaSourceFactory(applicationContext)
             .setExternalImageLoader(
-                unused -> listeningExecutorService.submit(loadingComplete::blockUninterruptible));
+                unused ->
+                    listeningExecutorService.submit(() -> loadingComplete.blockUninterruptible()));
     ExoPlayer player =
         new ExoPlayer.Builder(applicationContext, renderersFactory)
             .setClock(new FakeClock(/* isAutoAdvancing= */ true))

libraries/transformer/src/androidTest/java/androidx/media3/transformer/TransformerGapsTest.java

@@ -24,6 +24,8 @@ import static org.junit.Assert.assertThrows;
 import android.content.Context;
 import androidx.media3.common.C;
 import androidx.media3.common.MediaItem;
+import androidx.media3.common.MimeTypes;
+import androidx.media3.effect.Presentation;
 import androidx.media3.extractor.mp4.Mp4Extractor;
 import androidx.media3.extractor.text.DefaultSubtitleParserFactory;
 import androidx.media3.test.utils.FakeExtractorOutput;
@@ -31,6 +33,7 @@ import androidx.media3.test.utils.FakeTrackOutput;
 import androidx.media3.test.utils.TestUtil;
 import androidx.test.core.app.ApplicationProvider;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.google.common.collect.ImmutableList;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -60,7 +63,6 @@ public class TransformerGapsTest {
     testId = testName.getMethodName();
   }
 
-  // TODO: b/391111085 - Change test when gaps at the start of the sequence are supported.
   @Test
   public void export_withThreeMediaItemsAndFirstMediaItemHavingNoVideo_throws() {
     Transformer transformer = new Transformer.Builder(context).build();
@@ -77,6 +79,58 @@ public class TransformerGapsTest {
         ExportException.class, () -> transformerAndroidTestRunner.run(testId, composition));
   }
 
+  @Test
+  public void
+      export_withThreeMediaItemsAndFirstMediaItemHavingNoVideoAndForceVideoTrackSetToTrue_insertsBlankFramesForFirstMediaItem()
+          throws Exception {
+    int outputWidth = 320;
+    int outputHeight = 240;
+    assumeFormatsSupported(
+        context,
+        testId,
+        /* inputFormat= */ MP4_ASSET.videoFormat,
+        /* outputFormat= */ MP4_ASSET
+            .videoFormat
+            .buildUpon()
+            .setWidth(outputWidth)
+            .setHeight(outputHeight)
+            .build());
+    assumeFormatsSupported(
+        context,
+        testId,
+        /* inputFormat= */ MP4_ASSET.videoFormat,
+        /* outputFormat= */ MP4_ASSET.videoFormat);
+    Transformer transformer =
+        new Transformer.Builder(context).setVideoMimeType(MimeTypes.VIDEO_H264).build();
+    Composition composition =
+        new Composition.Builder(
+                new EditedMediaItemSequence.Builder(
+                        AUDIO_ONLY_MEDIA_ITEM, AUDIO_VIDEO_MEDIA_ITEM, AUDIO_VIDEO_MEDIA_ITEM)
+                    .setForceVideoTrack(true)
+                    .build())
+            .setEffects(
+                new Effects(
+                    ImmutableList.of(),
+                    ImmutableList.of(
+                        Presentation.createForWidthAndHeight(
+                            outputWidth, outputHeight, Presentation.LAYOUT_SCALE_TO_FIT))))
+            .build();
+
+    ExportTestResult result =
+        new TransformerAndroidTestRunner.Builder(context, transformer)
+            .build()
+            .run(testId, composition);
+
+    FakeExtractorOutput fakeExtractorOutput =
+        TestUtil.extractAllSamplesFromFilePath(
+            new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
+    FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
+    // The video gap is for 1024 ms with 30 fps.
+    int expectedBlankFrames = 31;
+    assertThat(videoTrackOutput.getSampleCount())
+        .isEqualTo(2 * MP4_ASSET.videoFrameCount + expectedBlankFrames);
+  }
+
   @Test
   public void
       export_withThreeMediaItemsAndSecondMediaItemHavingNoVideo_insertsBlankFramesForSecondMediaItem()
@@ -100,7 +154,7 @@ public class TransformerGapsTest {
         TestUtil.extractAllSamplesFromFilePath(
             new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
     FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
-    // The gap is for 1024ms with 30 fps.
+    // The gap is for 1024 ms with 30 fps.
     int expectedBlankFrames = 31;
     assertThat(videoTrackOutput.getSampleCount())
         .isEqualTo(2 * MP4_ASSET.videoFrameCount + expectedBlankFrames);
@@ -129,12 +183,62 @@ public class TransformerGapsTest {
         TestUtil.extractAllSamplesFromFilePath(
             new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
     FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
-    // The gap is for 1024ms with 30 fps.
+    // The gap is for 1024 ms with 30 fps.
     int expectedBlankFrames = 31;
     assertThat(videoTrackOutput.getSampleCount())
         .isEqualTo(2 * MP4_ASSET.videoFrameCount + expectedBlankFrames);
   }
 
+  @Test
+  public void
+      export_withTwoVideoOnlyMediaItemsAndGapAtStartAndForceVideoTrackSetToTrue_insertsBlankFramesForGap()
+          throws Exception {
+    int outputWidth = 320;
+    int outputHeight = 240;
+    assumeFormatsSupported(
+        context,
+        testId,
+        /* inputFormat= */ MP4_ASSET.videoFormat,
+        /* outputFormat= */ MP4_ASSET
+            .videoFormat
+            .buildUpon()
+            .setWidth(outputWidth)
+            .setHeight(outputHeight)
+            .build());
+    // The default output mime type is H265 which might not work on all the devices.
+    Transformer transformer =
+        new Transformer.Builder(context).setVideoMimeType(MimeTypes.VIDEO_H264).build();
+    Composition composition =
+        new Composition.Builder(
+                new EditedMediaItemSequence.Builder()
+                    .addGap(/* durationUs= */ 1_000_000)
+                    .addItem(VIDEO_ONLY_MEDIA_ITEM)
+                    .addItem(VIDEO_ONLY_MEDIA_ITEM)
+                    .setForceVideoTrack(true)
+                    .build())
+            .setEffects(
+                new Effects(
+                    ImmutableList.of(),
+                    ImmutableList.of(
+                        Presentation.createForWidthAndHeight(
+                            outputWidth, outputHeight, Presentation.LAYOUT_SCALE_TO_FIT))))
+            .build();
+
+    ExportTestResult result =
+        new TransformerAndroidTestRunner.Builder(context, transformer)
+            .build()
+            .run(testId, composition);
+
+    FakeExtractorOutput fakeExtractorOutput =
+        TestUtil.extractAllSamplesFromFilePath(
+            new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
+    FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
+    // The gap is for 1 sec with 30 fps.
+    int expectedBlankFrames = 30;
+    assertThat(videoTrackOutput.getSampleCount())
+        .isEqualTo(2 * MP4_ASSET.videoFrameCount + expectedBlankFrames);
+  }
+
   @Test
   public void export_withTwoVideoOnlyMediaItemsAndGapInMiddle_insertsBlankFramesForGap()
       throws Exception {
@@ -212,6 +316,83 @@ public class TransformerGapsTest {
     assertThrows(IllegalArgumentException.class, sequenceBuilder::build);
   }
 
+  @Test
+  public void export_withTwoMediaItemsAndGapAtStartAndOnlyForceAudioTrackSetToTrue_throws()
+      throws Exception {
+    Transformer transformer = new Transformer.Builder(context).build();
+    Composition composition =
+        new Composition.Builder(
+                new EditedMediaItemSequence.Builder()
+                    .addGap(/* durationUs= */ 1_000_000)
+                    .addItem(AUDIO_VIDEO_MEDIA_ITEM)
+                    .addItem(AUDIO_VIDEO_MEDIA_ITEM)
+                    .setForceAudioTrack(true)
+                    .build())
+            .build();
+    TransformerAndroidTestRunner transformerAndroidTestRunner =
+        new TransformerAndroidTestRunner.Builder(context, transformer).build();
+
+    assertThrows(
+        ExportException.class, () -> transformerAndroidTestRunner.run(testId, composition));
+  }
+
+  @Test
+  public void
+      export_withTwoMediaItemsAndGapAtStartAndBothForceAudioAndVideoTrackSetToTrue_insertsBlankFramesAndSilenceForGap()
+          throws Exception {
+    int outputWidth = 320;
+    int outputHeight = 240;
+    assumeFormatsSupported(
+        context,
+        testId,
+        /* inputFormat= */ MP4_ASSET.videoFormat,
+        /* outputFormat= */ MP4_ASSET
+            .videoFormat
+            .buildUpon()
+            .setWidth(outputWidth)
+            .setHeight(outputHeight)
+            .build());
+    // The default output mime type is H265 which might not work on all the devices.
+    Transformer transformer =
+        new Transformer.Builder(context).setVideoMimeType(MimeTypes.VIDEO_H264).build();
+    Composition composition =
+        new Composition.Builder(
+                new EditedMediaItemSequence.Builder()
+                    .addGap(/* durationUs= */ 1_000_000)
+                    .addItem(AUDIO_VIDEO_MEDIA_ITEM)
+                    .addItem(AUDIO_VIDEO_MEDIA_ITEM)
+                    .setForceAudioTrack(true)
+                    .setForceVideoTrack(true)
+                    .build())
+            .setEffects(
+                new Effects(
+                    ImmutableList.of(),
+                    ImmutableList.of(
+                        Presentation.createForWidthAndHeight(
+                            outputWidth, outputHeight, Presentation.LAYOUT_SCALE_TO_FIT))))
+            .build();
+
+    ExportTestResult result =
+        new TransformerAndroidTestRunner.Builder(context, transformer)
+            .build()
+            .run(testId, composition);
+
+    FakeExtractorOutput fakeExtractorOutput =
+        TestUtil.extractAllSamplesFromFilePath(
+            new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
+    FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
+    // The gap is for 1 sec with 30 fps.
+    int expectedBlankFrames = 30;
+    assertThat(videoTrackOutput.getSampleCount())
+        .isEqualTo(2 * MP4_ASSET.videoFrameCount + expectedBlankFrames);
+    FakeTrackOutput audioTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_AUDIO);
+    long lastAudioSampleTimestampUs =
+        audioTrackOutput.getSampleTimeUs(audioTrackOutput.getSampleCount() - 1);
+    // 1000 ms gap + 1024 ms audio + 1024 ms audio.
+    // Since audio samples are not deterministic, hence use a lower timestamp.
+    assertThat(lastAudioSampleTimestampUs).isGreaterThan(3_000_000);
+  }
+
   @Test
   public void export_withTwoMediaItemsAndGapInMiddle_insertsBlankFramesForGap() throws Exception {
     assumeFormatsSupported(
@@ -303,7 +484,7 @@ public class TransformerGapsTest {
         TestUtil.extractAllSamplesFromFilePath(
             new Mp4Extractor(new DefaultSubtitleParserFactory()), result.filePath);
     FakeTrackOutput videoTrackOutput = getTrackOutput(fakeExtractorOutput, C.TRACK_TYPE_VIDEO);
-    // The gap is for 1024ms with 30 fps.
+    // The gap is for 1024 ms with 30 fps.
     int expectedBlankFramesForAudioOnlyItem = 31;
     // The gap is for 1 sec with 30 fps.
     int expectedBlankFramesForOneSecGap = 30;

libraries/transformer/src/main/java/androidx/media3/transformer/EditedMediaItemSequence.java

@@ -20,6 +20,7 @@ import static androidx.media3.common.util.Assertions.checkArgument;
 import androidx.media3.common.MediaItem;
 import androidx.media3.common.audio.AudioProcessor;
 import androidx.media3.common.util.UnstableApi;
+import androidx.media3.effect.Presentation;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.util.List;
@@ -37,6 +38,7 @@ public final class EditedMediaItemSequence {
     private final ImmutableList.Builder<EditedMediaItem> items;
     private boolean isLooping;
     private boolean forceAudioTrack;
+    private boolean forceVideoTrack;
 
     /** Creates an instance. */
     public Builder(EditedMediaItem... editedMediaItems) {
@@ -55,6 +57,7 @@ public final class EditedMediaItemSequence {
               .addAll(editedMediaItemSequence.editedMediaItems);
       isLooping = editedMediaItemSequence.isLooping;
       forceAudioTrack = editedMediaItemSequence.forceAudioTrack;
+      forceVideoTrack = editedMediaItemSequence.forceVideoTrack;
     }
 
     /**
@@ -98,10 +101,9 @@ public final class EditedMediaItemSequence {
      *
      * <p>A gap is a period of time with no media.
      *
-     * <p>If the gap is at the start of the sequence then {@linkplain #setForceAudioTrack(boolean)
-     * force audio track} flag must be set to force silent audio.
-     *
-     * <p>Gaps at the start of the sequence are not supported if the sequence has video.
+     * <p>If the gap is added at the start of the sequence, then {@linkplain
+     * #setForceAudioTrack(boolean) force audio track} or/and {@linkplain
+     * #setForceVideoTrack(boolean) force video track} flag must be set appropriately.
      *
      * @param durationUs The duration of the gap, in milliseconds.
      * @return This builder, for convenience.
@@ -165,6 +167,43 @@ public final class EditedMediaItemSequence {
       return this;
     }
 
+    /**
+     * Forces blank frames in the {@linkplain EditedMediaItemSequence sequence}.
+     *
+     * <p>This flag is necessary when:
+     *
+     * <ul>
+     *   <li>The first {@link EditedMediaItem} in the sequence does not contain video, but
+     *       subsequent items do.
+     *   <li>The first item in the sequence is a {@linkplain #addGap(long) gap} and the subsequent
+     *       {@linkplain EditedMediaItem media items} contain video.
+     * </ul>
+     *
+     * <p>If the flag is not set appropriately, then the export will {@linkplain
+     * Transformer.Listener#onError(Composition, ExportResult, ExportException) fail}.
+     *
+     * <p>If the first {@link EditedMediaItem} already contains video, this flag has no effect.
+     *
+     * <p>The MIME type of the output's video track can be set using {@link
+     * Transformer.Builder#setVideoMimeType(String)}.
+     *
+     * <p>The output resolution must be set using a {@link Presentation} effect on the {@link
+     * Composition}.
+     *
+     * <p>Forcing a video track and {@linkplain Composition.Builder#setTransmuxVideo(boolean)
+     * requesting video transmuxing} are not allowed together because generating blank frames
+     * requires transcoding.
+     *
+     * <p>The default value is {@code false}.
+     *
+     * @param forceVideoTrack Whether to force video track.
+     */
+    @CanIgnoreReturnValue
+    public Builder setForceVideoTrack(boolean forceVideoTrack) {
+      this.forceVideoTrack = forceVideoTrack;
+      return this;
+    }
+
     /**
      * Builds the {@link EditedMediaItemSequence}.
      *
@@ -199,6 +238,9 @@ public final class EditedMediaItemSequence {
   /** Forces silent audio in the {@linkplain EditedMediaItemSequence sequence}. */
   public final boolean forceAudioTrack;
 
+  /** Forces blank frames in the {@linkplain EditedMediaItemSequence sequence}. */
+  public final boolean forceVideoTrack;
+
   /**
    * @deprecated Use {@link Builder}.
    */
@@ -234,10 +276,12 @@ public final class EditedMediaItemSequence {
     checkArgument(
         !editedMediaItems.isEmpty(), "The sequence must contain at least one EditedMediaItem.");
     checkArgument(
-        !editedMediaItems.get(0).isGap() || builder.forceAudioTrack,
-        "If the first item in the sequence is a Gap, then forceAudioTrack flag must be set");
+        !editedMediaItems.get(0).isGap() || builder.forceAudioTrack || builder.forceVideoTrack,
+        "If the first item in the sequence is a Gap, then forceAudioTrack or forceVideoTrack flag"
+            + " must be set");
     this.isLooping = builder.isLooping;
     this.forceAudioTrack = builder.forceAudioTrack;
+    this.forceVideoTrack = builder.forceVideoTrack;
   }
 
   /** Return whether any items are a {@linkplain Builder#addGap(long) gap}. */

libraries/transformer/src/main/java/androidx/media3/transformer/SequenceAssetLoader.java

@@ -83,6 +83,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
   private final List<EditedMediaItem> editedMediaItems;
   private final boolean isLooping;
   private final boolean forceAudioTrack;
+  private final boolean forceVideoTrack;
   private final Factory assetLoaderFactory;
   private final CompositionSettings compositionSettings;
   private final Listener sequenceAssetLoaderListener;
@@ -139,6 +140,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     editedMediaItems = sequence.editedMediaItems;
     isLooping = sequence.isLooping;
     this.forceAudioTrack = sequence.forceAudioTrack;
+    this.forceVideoTrack = sequence.forceVideoTrack;
     this.assetLoaderFactory = new GapInterceptingAssetLoaderFactory(assetLoaderFactory);
     this.compositionSettings = compositionSettings;
     sequenceAssetLoaderListener = listener;
@@ -271,10 +273,16 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       return decode;
     }
 
-    boolean addForcedAudioTrack = forceAudioTrack && reportedTrackCount.get() == 1 && !isAudio;
+    boolean addForcedAudioTrack = false;
+    boolean addForcedVideoTrack = false;
+    if (reportedTrackCount.get() == 1) {
+      addForcedAudioTrack = forceAudioTrack && !isAudio;
+      addForcedVideoTrack = forceVideoTrack && isAudio;
+    }
 
     if (!isTrackCountReported) {
-      int trackCount = reportedTrackCount.get() + (addForcedAudioTrack ? 1 : 0);
+      int trackCount =
+          reportedTrackCount.get() + (addForcedAudioTrack || addForcedVideoTrack ? 1 : 0);
       sequenceAssetLoaderListener.onTrackCount(trackCount);
       isTrackCountReported = true;
     }
@@ -293,6 +301,11 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
           FORCE_AUDIO_TRACK_FORMAT, SUPPORTED_OUTPUT_TYPE_DECODED);
       decodeAudio = true;
     }
+    if (addForcedVideoTrack) {
+      sequenceAssetLoaderListener.onTrackAdded(
+          BLANK_IMAGE_BITMAP_FORMAT, SUPPORTED_OUTPUT_TYPE_DECODED);
+      decodeVideo = true;
+    }
 
     return decodeOutput;
   }
@@ -324,30 +337,41 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       sampleConsumer = new SampleConsumerWrapper(wrappedSampleConsumer, trackType);
       sampleConsumersByTrackType.put(trackType, sampleConsumer);
 
-      if (forceAudioTrack && reportedTrackCount.get() == 1 && trackType == C.TRACK_TYPE_VIDEO) {
-        SampleConsumer wrappedAudioSampleConsumer =
-            checkStateNotNull(
-                sequenceAssetLoaderListener.onOutputFormat(
-                    FORCE_AUDIO_TRACK_FORMAT
-                        .buildUpon()
-                        .setSampleMimeType(MimeTypes.AUDIO_RAW)
-                        .setPcmEncoding(C.ENCODING_PCM_16BIT)
-                        .build()));
-        sampleConsumersByTrackType.put(
-            C.TRACK_TYPE_AUDIO,
-            new SampleConsumerWrapper(wrappedAudioSampleConsumer, C.TRACK_TYPE_AUDIO));
+      if (reportedTrackCount.get() == 1) {
+        if (forceAudioTrack && trackType == C.TRACK_TYPE_VIDEO) {
+          SampleConsumer wrappedAudioSampleConsumer =
+              checkStateNotNull(
+                  sequenceAssetLoaderListener.onOutputFormat(
+                      FORCE_AUDIO_TRACK_FORMAT
+                          .buildUpon()
+                          .setSampleMimeType(MimeTypes.AUDIO_RAW)
+                          .setPcmEncoding(C.ENCODING_PCM_16BIT)
+                          .build()));
+          sampleConsumersByTrackType.put(
+              C.TRACK_TYPE_AUDIO,
+              new SampleConsumerWrapper(wrappedAudioSampleConsumer, C.TRACK_TYPE_AUDIO));
+        } else if (forceVideoTrack && trackType == C.TRACK_TYPE_AUDIO) {
+          SampleConsumer wrappedVideoSampleConsumer =
+              checkStateNotNull(
+                  sequenceAssetLoaderListener.onOutputFormat(BLANK_IMAGE_BITMAP_FORMAT));
+          sampleConsumersByTrackType.put(
+              C.TRACK_TYPE_VIDEO,
+              new SampleConsumerWrapper(wrappedVideoSampleConsumer, C.TRACK_TYPE_VIDEO));
+        }
       }
     } else {
+      String missingTrackMessage =
+          trackType == C.TRACK_TYPE_AUDIO
+              ? "The preceding MediaItem does not contain any audio track. If the sequence starts"
+                  + " with an item without audio track (like images), followed by items with"
+                  + " audio tracks, then EditedMediaItemSequence.Builder.setForceAudioTrack()"
+                  + " needs to be set to true."
+              : "The preceding MediaItem does not contain any video track. If the sequence starts"
+                  + " with an item without video track (audio only), followed by items with video"
+                  + " tracks, then EditedMediaItemSequence.Builder.setForceVideoTrack() needs to"
+                  + " be set to true.";
       sampleConsumer =
-          checkStateNotNull(
-              sampleConsumersByTrackType.get(trackType),
-              Util.formatInvariant(
-                  "The preceding MediaItem does not contain any track of type %d. If the"
-                      + " Composition contains a sequence that starts with items without audio"
-                      + " tracks (like images), followed by items with audio tracks,"
-                      + " Composition.Builder.experimentalSetForceAudioTrack() needs to be set to"
-                      + " true.",
-                  trackType));
+          checkStateNotNull(sampleConsumersByTrackType.get(trackType), missingTrackMessage);
     }
     onMediaItemChanged(trackType, format);
     if (reportedTrackCount.get() == 1 && sampleConsumersByTrackType.size() == 2) {
@@ -700,7 +724,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     private GapSignalingAssetLoader(long durationUs) {
       this.durationUs = durationUs;
       shouldProduceAudio = sequenceHasAudio || forceAudioTrack;
-      shouldProduceVideo = sequenceHasVideo;
+      shouldProduceVideo = sequenceHasVideo || forceVideoTrack;
       checkState(shouldProduceAudio || shouldProduceVideo);
       this.audioTrackFormat = new Format.Builder().setSampleMimeType(MimeTypes.AUDIO_RAW).build();
       this.audioTrackDecodedFormat =