Configure AudioProcessingPipeline with the current pendingStartTimeUs

Before this change, AudioGraph would ignore the last set
pendingStartTimeUs when configuring the AudioProcessingPipeline for the
first time, which happens when the AudioGraph registers its first input.

PiperOrigin-RevId: 785868112

Author: ivanbuper

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

@@ -80,8 +80,6 @@ public static boolean isInputAudioFormatValid(AudioFormat format) {
   /**
    * Returns a new {@link AudioGraphInput} instance.
    *
-   * <p>This method assumes the new input will start queueing its stream from the beginning.
-   *
    * <p>Must be called before {@linkplain #getOutput() accessing output}.
    */
   public AudioGraphInput registerInput(EditedMediaItem editedMediaItem, Format format)
@@ -93,7 +91,7 @@ public AudioGraphInput registerInput(EditedMediaItem editedMediaItem, Format for
       if (Objects.equals(mixerAudioFormat, AudioFormat.NOT_SET)) {
         this.mixerAudioFormat = audioGraphInput.getOutputAudioFormat();
         audioProcessingPipeline.configure(mixerAudioFormat);
-        audioProcessingPipeline.flush(new StreamMetadata(/* positionOffsetUs= */ 0));
+        audioProcessingPipeline.flush(new StreamMetadata(pendingStartTimeUs));
       }
     } catch (UnhandledAudioFormatException e) {
       throw ExportException.createForAudioProcessing(
@@ -122,7 +120,7 @@ public AudioFormat getOutputAudioFormat() {
    * Returns a {@link ByteBuffer} containing output data between the position and limit.
    *
    * <p>The same buffer is returned until it has been fully consumed ({@code position == limit}),
-   * unless the graph was {@linkplain #flush() flushed}.
+   * unless the graph was {@linkplain #flush flushed}.
    */
   public ByteBuffer getOutput() throws ExportException {
     if (!ensureMixerReady()) {

libraries/transformer/src/test/java/androidx/media3/transformer/AudioGraphTest.java

@@ -463,6 +463,70 @@ protected void onFlush(StreamMetadata streamMetadata) {
     assertThat(lastPositionOffsetUs.get()).isEqualTo(500_000);
   }
 
+  @Test
+  public void flush_beforeRegisteringFirstInput_maintainsPreviousPositionOffset() throws Exception {
+    AtomicLong lastPositionOffsetUs = new AtomicLong(C.TIME_UNSET);
+    BaseAudioProcessor fakeProcessor =
+        new PassthroughAudioProcessor() {
+          @Override
+          protected void onFlush(StreamMetadata streamMetadata) {
+            lastPositionOffsetUs.set(streamMetadata.positionOffsetUs);
+          }
+        };
+    AudioGraph audioGraph =
+        new AudioGraph(
+            new DefaultAudioMixer.Factory(), /* effects= */ ImmutableList.of(fakeProcessor));
+
+    audioGraph.flush(/* positionOffsetUs= */ 500_000);
+    lastPositionOffsetUs.set(C.TIME_UNSET);
+    audioGraph.registerInput(FAKE_ITEM, getPcmFormat(MONO_44100));
+
+    assertThat(lastPositionOffsetUs.get()).isEqualTo(500_000);
+  }
+
+  @Test
+  public void flush_multipleTimes_propagatesLastPositionOffsetAfterFirstInput() throws Exception {
+    AtomicLong lastPositionOffsetUs = new AtomicLong(C.TIME_UNSET);
+    BaseAudioProcessor fakeProcessor =
+        new PassthroughAudioProcessor() {
+          @Override
+          protected void onFlush(StreamMetadata streamMetadata) {
+            lastPositionOffsetUs.set(streamMetadata.positionOffsetUs);
+          }
+        };
+    AudioGraph audioGraph =
+        new AudioGraph(
+            new DefaultAudioMixer.Factory(), /* effects= */ ImmutableList.of(fakeProcessor));
+
+    audioGraph.flush(/* positionOffsetUs= */ 500_000);
+    audioGraph.flush(/* positionOffsetUs= */ 600_000);
+    audioGraph.flush(/* positionOffsetUs= */ 700_000);
+    audioGraph.registerInput(FAKE_ITEM, getPcmFormat(MONO_44100));
+
+    assertThat(lastPositionOffsetUs.get()).isEqualTo(700_000);
+  }
+
+  @Test
+  public void flush_afterRegisteringFirstInput_updatesPositionOffset() throws Exception {
+    AtomicLong lastPositionOffsetUs = new AtomicLong(C.TIME_UNSET);
+    BaseAudioProcessor fakeProcessor =
+        new PassthroughAudioProcessor() {
+          @Override
+          protected void onFlush(StreamMetadata streamMetadata) {
+            lastPositionOffsetUs.set(streamMetadata.positionOffsetUs);
+          }
+        };
+    AudioGraph audioGraph =
+        new AudioGraph(
+            new DefaultAudioMixer.Factory(), /* effects= */ ImmutableList.of(fakeProcessor));
+
+    audioGraph.registerInput(FAKE_ITEM, getPcmFormat(MONO_44100));
+    assertThat(lastPositionOffsetUs.get()).isEqualTo(0);
+    audioGraph.flush(/* positionOffsetUs= */ 500_000);
+
+    assertThat(lastPositionOffsetUs.get()).isEqualTo(500_000);
+  }
+
   /** Drains the graph and returns the number of bytes output. */
   private static int drainAudioGraph(AudioGraph audioGraph) throws ExportException {
     int bytesOutput = 0;