Add PassthroughSamplePipeline for audio.

When no transformation is needed, the passthrough pipeline allows us to skip decoding and re-encoding.

PiperOrigin-RevId: 407789767

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioSamplePipeline.java

@@ -366,6 +366,7 @@ private ExoPlaybackException createRendererException(Throwable cause, int errorC
         errorCode);
   }
 
+  // TODO(internal b/204978301): Ensure encoder and decoder timestamps match when no speed change.
   private static long getBufferDurationUs(long bytesWritten, int bytesPerFrame, int sampleRate) {
     long framesWritten = bytesWritten / bytesPerFrame;
     return framesWritten * C.MICROS_PER_SECOND / sampleRate;

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/PassthroughSamplePipeline.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2021 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.transformer;
+
+import androidx.annotation.Nullable;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
+
+/** Pipeline that passes through the samples without any re-encoding or transformation. */
+/* package */ final class PassthroughSamplePipeline implements SamplePipeline {
+
+  private final DecoderInputBuffer buffer;
+  private final Format format;
+
+  private boolean hasPendingBuffer;
+
+  public PassthroughSamplePipeline(Format format) {
+    this.format = format;
+    buffer = new DecoderInputBuffer(DecoderInputBuffer.BUFFER_REPLACEMENT_MODE_DIRECT);
+    hasPendingBuffer = false;
+  }
+
+  @Override
+  @Nullable
+  public DecoderInputBuffer dequeueInputBuffer() {
+    return hasPendingBuffer ? null : buffer;
+  }
+
+  @Override
+  public void queueInputBuffer() {
+    hasPendingBuffer = true;
+  }
+
+  @Override
+  public boolean processData() {
+    return false;
+  }
+
+  @Override
+  public Format getOutputFormat() {
+    return format;
+  }
+
+  @Override
+  @Nullable
+  public DecoderInputBuffer getOutputBuffer() {
+    return hasPendingBuffer ? buffer : null;
+  }
+
+  @Override
+  public void releaseOutputBuffer() {
+    buffer.clear();
+    hasPendingBuffer = false;
+  }
+
+  @Override
+  public boolean isEnded() {
+    return buffer.isEndOfStream();
+  }
+
+  @Override
+  public void release() {}
+}

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerAudioRenderer.java

@@ -89,8 +89,14 @@ private boolean ensureRendererConfigured() throws ExoPlaybackException {
     if (result != C.RESULT_FORMAT_READ) {
       return false;
     }
-    samplePipeline =
-        new AudioSamplePipeline(checkNotNull(formatHolder.format), transformation, getIndex());
+    Format decoderInputFormat = checkNotNull(formatHolder.format);
+    if ((transformation.audioMimeType != null
+            && !transformation.audioMimeType.equals(decoderInputFormat.sampleMimeType))
+        || transformation.flattenForSlowMotion) {
+      samplePipeline = new AudioSamplePipeline(decoderInputFormat, transformation, getIndex());
+    } else {
+      samplePipeline = new PassthroughSamplePipeline(decoderInputFormat);
+    }
     return true;
   }