diff --git a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioSamplePipeline.java b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioTranscodingSamplePipeline.java
similarity index 93%
rename from library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioSamplePipeline.java
rename to library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioTranscodingSamplePipeline.java
index f42ec06340..60d5be779c 100644
--- a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioSamplePipeline.java
+++ b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/AudioTranscodingSamplePipeline.java
@@ -18,7 +18,6 @@ package com.google.android.exoplayer2.transformer;
 
 import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
 import static com.google.android.exoplayer2.util.Assertions.checkState;
-import static com.google.android.exoplayer2.util.Assertions.checkStateNotNull;
 import static java.lang.Math.min;
 
 import android.media.MediaCodec.BufferInfo;
@@ -37,9 +36,8 @@ import org.checkerframework.dataflow.qual.Pure;
 /**
  * Pipeline to decode audio samples, apply transformations on the raw samples, and re-encode them.
  */
-/* package */ final class AudioSamplePipeline implements SamplePipeline {
+/* package */ final class AudioTranscodingSamplePipeline implements SamplePipeline {
 
-  private static final String TAG = "AudioSamplePipeline";
   private static final int DEFAULT_ENCODER_BITRATE = 128 * 1024;
 
   private final Codec decoder;
@@ -61,7 +59,7 @@ import org.checkerframework.dataflow.qual.Pure;
   private boolean drainingSonicForSpeedChange;
   private float currentSpeed;
 
-  public AudioSamplePipeline(
+  public AudioTranscodingSamplePipeline(
       Format inputFormat,
       TransformationRequest transformationRequest,
       Codec.DecoderFactory decoderFactory,
@@ -142,40 +140,36 @@ import org.checkerframework.dataflow.qual.Pure;
   @Override
   @Nullable
   public Format getOutputFormat() throws TransformationException {
-    return encoder != null ? encoder.getOutputFormat() : null;
+    return encoder.getOutputFormat();
   }
 
   @Override
   @Nullable
   public DecoderInputBuffer getOutputBuffer() throws TransformationException {
-    if (encoder != null) {
-      encoderOutputBuffer.data = encoder.getOutputBuffer();
-      if (encoderOutputBuffer.data != null) {
-        encoderOutputBuffer.timeUs = checkNotNull(encoder.getOutputBufferInfo()).presentationTimeUs;
-        encoderOutputBuffer.setFlags(C.BUFFER_FLAG_KEY_FRAME);
-        return encoderOutputBuffer;
-      }
+    encoderOutputBuffer.data = encoder.getOutputBuffer();
+    if (encoderOutputBuffer.data == null) {
+      return null;
     }
-    return null;
+    encoderOutputBuffer.timeUs = checkNotNull(encoder.getOutputBufferInfo()).presentationTimeUs;
+    encoderOutputBuffer.setFlags(C.BUFFER_FLAG_KEY_FRAME);
+    return encoderOutputBuffer;
   }
 
   @Override
   public void releaseOutputBuffer() throws TransformationException {
-    checkStateNotNull(encoder).releaseOutputBuffer();
+    encoder.releaseOutputBuffer();
   }
 
   @Override
   public boolean isEnded() {
-    return encoder != null && encoder.isEnded();
+    return encoder.isEnded();
   }
 
   @Override
   public void release() {
     sonicAudioProcessor.reset();
     decoder.release();
-    if (encoder != null) {
-      encoder.release();
-    }
+    encoder.release();
   }
 
   /**
diff --git a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/Transformer.java b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/Transformer.java
index f312d84643..20caac1ea8 100644
--- a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/Transformer.java
+++ b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/Transformer.java
@@ -917,7 +917,7 @@ public final class Transformer {
 
     @Override
     public void onPlayerError(PlaybackException error) {
-      Throwable cause = error.getCause();
+      @Nullable Throwable cause = error.getCause();
       handleTransformationEnded(
           cause instanceof TransformationException
               ? (TransformationException) cause
diff --git a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerAudioRenderer.java b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerAudioRenderer.java
index 73701f6589..f5fb4a7971 100644
--- a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerAudioRenderer.java
+++ b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerAudioRenderer.java
@@ -73,7 +73,7 @@ import com.google.android.exoplayer2.source.SampleStream.ReadDataResult;
           new PassthroughSamplePipeline(inputFormat, transformationRequest, fallbackListener);
     } else {
       samplePipeline =
-          new AudioSamplePipeline(
+          new AudioTranscodingSamplePipeline(
               inputFormat,
               transformationRequest,
               decoderFactory,
diff --git a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerVideoRenderer.java b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerVideoRenderer.java
index 7c12f87bd5..062fecb0ab 100644
--- a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerVideoRenderer.java
+++ b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerVideoRenderer.java
@@ -82,7 +82,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
           new PassthroughSamplePipeline(inputFormat, transformationRequest, fallbackListener);
     } else {
       samplePipeline =
-          new VideoSamplePipeline(
+          new VideoTranscodingSamplePipeline(
               context,
               inputFormat,
               transformationRequest,
diff --git a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoSamplePipeline.java b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoTranscodingSamplePipeline.java
similarity index 98%
rename from library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoSamplePipeline.java
rename to library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoTranscodingSamplePipeline.java
index 7fd12dfa10..32bbca3e43 100644
--- a/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoSamplePipeline.java
+++ b/library/transformer/src/main/java/com/google/android/exoplayer2/transformer/VideoTranscodingSamplePipeline.java
@@ -36,9 +36,7 @@ import org.checkerframework.dataflow.qual.Pure;
 /**
  * Pipeline to decode video samples, apply transformations on the raw samples, and re-encode them.
  */
-/* package */ final class VideoSamplePipeline implements SamplePipeline {
-
-  private static final String TAG = "VideoSamplePipeline";
+/* package */ final class VideoTranscodingSamplePipeline implements SamplePipeline {
 
   private final int outputRotationDegrees;
   private final DecoderInputBuffer decoderInputBuffer;
@@ -51,7 +49,7 @@ import org.checkerframework.dataflow.qual.Pure;
 
   private boolean waitingForFrameEditorInput;
 
-  public VideoSamplePipeline(
+  public VideoTranscodingSamplePipeline(
       Context context,
       Format inputFormat,
       TransformationRequest transformationRequest,
@@ -233,7 +231,7 @@ import org.checkerframework.dataflow.qual.Pure;
   @Override
   @Nullable
   public Format getOutputFormat() throws TransformationException {
-    Format format = encoder.getOutputFormat();
+    @Nullable Format format = encoder.getOutputFormat();
     return format == null
         ? null
         : format.buildUpon().setRotationDegrees(outputRotationDegrees).build();