Support mu-law and A-law PCM with ffmpeg

Issue: #4360

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=200186465

RELEASENOTES.md

@@ -27,6 +27,8 @@
   ([#4023](https://github.com/google/ExoPlayer/issues/4023)).
 * Allow apps to register custom MIME types
   ([#4264](https://github.com/google/ExoPlayer/issues/4264)).
+* Add support for mu-law and A-law PCM with the ffmpeg extension
+  ([#4360](https://github.com/google/ExoPlayer/issues/4360)).
 
 ### 2.8.2 ###
 

extensions/ffmpeg/build.gradle

@@ -37,6 +37,8 @@ android {
 
 dependencies {
     implementation project(modulePrefix + 'library-core')
+    implementation 'com.android.support:support-annotations:' + supportLibraryVersion
+    compileOnly 'org.checkerframework:checker-qual:' + checkerframeworkVersion
 }
 
 ext {

extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegAudioRenderer.java

@@ -16,6 +16,7 @@
 package com.google.android.exoplayer2.ext.ffmpeg;
 
 import android.os.Handler;
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlaybackException;
 import com.google.android.exoplayer2.Format;
@@ -26,7 +27,10 @@ import com.google.android.exoplayer2.audio.DefaultAudioSink;
 import com.google.android.exoplayer2.audio.SimpleDecoderAudioRenderer;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.ExoMediaCrypto;
+import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.MimeTypes;
+import java.util.Collections;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /**
  * Decodes and renders audio using FFmpeg.
@@ -45,10 +49,10 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
 
   private final boolean enableFloatOutput;
 
-  private FfmpegDecoder decoder;
+  private @MonotonicNonNull FfmpegDecoder decoder;
 
   public FfmpegAudioRenderer() {
-    this(null, null);
+    this(/* eventHandler= */ null, /* eventListener= */ null);
   }
 
   /**
@@ -57,9 +61,15 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
    * @param eventListener A listener of events. May be null if delivery of events is not required.
    * @param audioProcessors Optional {@link AudioProcessor}s that will process audio before output.
    */
-  public FfmpegAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
+  public FfmpegAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
       AudioProcessor... audioProcessors) {
-    this(eventHandler, eventListener, new DefaultAudioSink(null, audioProcessors), false);
+    this(
+        eventHandler,
+        eventListener,
+        new DefaultAudioSink(/* audioCapabilities= */ null, audioProcessors),
+        /* enableFloatOutput= */ false);
   }
 
   /**
@@ -72,8 +82,11 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
    *     32-bit float output, any audio processing will be disabled, including playback speed/pitch
    *     adjustment.
    */
-  public FfmpegAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
-      AudioSink audioSink, boolean enableFloatOutput) {
+  public FfmpegAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
+      AudioSink audioSink,
+      boolean enableFloatOutput) {
     super(
         eventHandler,
         eventListener,
@@ -86,10 +99,11 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
   @Override
   protected int supportsFormatInternal(DrmSessionManager<ExoMediaCrypto> drmSessionManager,
       Format format) {
-    String sampleMimeType = format.sampleMimeType;
-    if (!FfmpegLibrary.isAvailable() || !MimeTypes.isAudio(sampleMimeType)) {
+    Assertions.checkNotNull(format.sampleMimeType);
+    if (!FfmpegLibrary.isAvailable() || !MimeTypes.isAudio(format.sampleMimeType)) {
       return FORMAT_UNSUPPORTED_TYPE;
-    } else if (!FfmpegLibrary.supportsFormat(sampleMimeType) || !isOutputSupported(format)) {
+    } else if (!FfmpegLibrary.supportsFormat(format.sampleMimeType, format.pcmEncoding)
+        || !isOutputSupported(format)) {
       return FORMAT_UNSUPPORTED_SUBTYPE;
     } else if (!supportsFormatDrm(drmSessionManager, format.drmInitData)) {
       return FORMAT_UNSUPPORTED_DRM;
@@ -106,18 +120,35 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
   @Override
   protected FfmpegDecoder createDecoder(Format format, ExoMediaCrypto mediaCrypto)
       throws FfmpegDecoderException {
-    decoder = new FfmpegDecoder(NUM_BUFFERS, NUM_BUFFERS, INITIAL_INPUT_BUFFER_SIZE,
-        format.sampleMimeType, format.initializationData, shouldUseFloatOutput(format));
+    decoder =
+        new FfmpegDecoder(
+            NUM_BUFFERS,
+            NUM_BUFFERS,
+            INITIAL_INPUT_BUFFER_SIZE,
+            format,
+            shouldUseFloatOutput(format));
     return decoder;
   }
 
   @Override
   public Format getOutputFormat() {
+    Assertions.checkNotNull(decoder);
     int channelCount = decoder.getChannelCount();
     int sampleRate = decoder.getSampleRate();
     @C.PcmEncoding int encoding = decoder.getEncoding();
-    return Format.createAudioSampleFormat(null, MimeTypes.AUDIO_RAW, null, Format.NO_VALUE,
-        Format.NO_VALUE, channelCount, sampleRate, encoding, null, null, 0, null);
+    return Format.createAudioSampleFormat(
+        /* id= */ null,
+        MimeTypes.AUDIO_RAW,
+        /* codecs= */ null,
+        Format.NO_VALUE,
+        Format.NO_VALUE,
+        channelCount,
+        sampleRate,
+        encoding,
+        Collections.emptyList(),
+        /* drmInitData= */ null,
+        /* selectionFlags= */ 0,
+        /* language= */ null);
   }
 
   private boolean isOutputSupported(Format inputFormat) {
@@ -125,6 +156,7 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
   }
 
   private boolean shouldUseFloatOutput(Format inputFormat) {
+    Assertions.checkNotNull(inputFormat.sampleMimeType);
     if (!enableFloatOutput || !supportsOutputEncoding(C.ENCODING_PCM_FLOAT)) {
       return false;
     }

extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegDecoder.java

@@ -15,10 +15,13 @@
  */
 package com.google.android.exoplayer2.ext.ffmpeg;
 
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
 import com.google.android.exoplayer2.decoder.SimpleDecoder;
 import com.google.android.exoplayer2.decoder.SimpleOutputBuffer;
+import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.MimeTypes;
 import com.google.android.exoplayer2.util.ParsableByteArray;
 import java.nio.ByteBuffer;
@@ -30,13 +33,12 @@ import java.util.List;
 /* package */ final class FfmpegDecoder extends
     SimpleDecoder<DecoderInputBuffer, SimpleOutputBuffer, FfmpegDecoderException> {
 
-  // Space for 64 ms of 48 kHz 8 channel 16-bit PCM audio.
-  private static final int OUTPUT_BUFFER_SIZE_16BIT = 64 * 48  * 8 * 2;
-  // Space for 64 ms of 48 KhZ 8 channel 32-bit PCM audio.
+  // Output buffer sizes when decoding PCM mu-law streams, which is the maximum FFmpeg outputs.
+  private static final int OUTPUT_BUFFER_SIZE_16BIT = 65536;
   private static final int OUTPUT_BUFFER_SIZE_32BIT = OUTPUT_BUFFER_SIZE_16BIT * 2;
 
   private final String codecName;
-  private final byte[] extraData;
+  private final @Nullable byte[] extraData;
   private final @C.Encoding int encoding;
   private final int outputBufferSize;
 
@@ -45,18 +47,26 @@ import java.util.List;
   private volatile int channelCount;
   private volatile int sampleRate;
 
-  public FfmpegDecoder(int numInputBuffers, int numOutputBuffers, int initialInputBufferSize,
-      String mimeType, List<byte[]> initializationData, boolean outputFloat)
+  public FfmpegDecoder(
+      int numInputBuffers,
+      int numOutputBuffers,
+      int initialInputBufferSize,
+      Format format,
+      boolean outputFloat)
       throws FfmpegDecoderException {
     super(new DecoderInputBuffer[numInputBuffers], new SimpleOutputBuffer[numOutputBuffers]);
     if (!FfmpegLibrary.isAvailable()) {
       throw new FfmpegDecoderException("Failed to load decoder native libraries.");
     }
-    codecName = FfmpegLibrary.getCodecName(mimeType);
-    extraData = getExtraData(mimeType, initializationData);
+    Assertions.checkNotNull(format.sampleMimeType);
+    codecName =
+        Assertions.checkNotNull(
+            FfmpegLibrary.getCodecName(format.sampleMimeType, format.pcmEncoding));
+    extraData = getExtraData(format.sampleMimeType, format.initializationData);
     encoding = outputFloat ? C.ENCODING_PCM_FLOAT : C.ENCODING_PCM_16BIT;
     outputBufferSize = outputFloat ? OUTPUT_BUFFER_SIZE_32BIT : OUTPUT_BUFFER_SIZE_16BIT;
-    nativeContext = ffmpegInitialize(codecName, extraData, outputFloat);
+    nativeContext =
+        ffmpegInitialize(codecName, extraData, outputFloat, format.sampleRate, format.channelCount);
     if (nativeContext == 0) {
       throw new FfmpegDecoderException("Initialization failed.");
     }
@@ -84,7 +94,7 @@ import java.util.List;
   }
 
   @Override
-  protected FfmpegDecoderException decode(
+  protected @Nullable FfmpegDecoderException decode(
       DecoderInputBuffer inputBuffer, SimpleOutputBuffer outputBuffer, boolean reset) {
     if (reset) {
       nativeContext = ffmpegReset(nativeContext, extraData);
@@ -103,6 +113,7 @@ import java.util.List;
       channelCount = ffmpegGetChannelCount(nativeContext);
       sampleRate = ffmpegGetSampleRate(nativeContext);
       if (sampleRate == 0 && "alac".equals(codecName)) {
+        Assertions.checkNotNull(extraData);
         // ALAC decoder did not set the sample rate in earlier versions of FFMPEG.
         // See https://trac.ffmpeg.org/ticket/6096
         ParsableByteArray parsableExtraData = new ParsableByteArray(extraData);
@@ -148,7 +159,7 @@ import java.util.List;
    * Returns FFmpeg-compatible codec-specific initialization data ("extra data"), or {@code null} if
    * not required.
    */
-  private static byte[] getExtraData(String mimeType, List<byte[]> initializationData) {
+  private static @Nullable byte[] getExtraData(String mimeType, List<byte[]> initializationData) {
     switch (mimeType) {
       case MimeTypes.AUDIO_AAC:
       case MimeTypes.AUDIO_ALAC:
@@ -173,12 +184,20 @@ import java.util.List;
     }
   }
 
-  private native long ffmpegInitialize(String codecName, byte[] extraData, boolean outputFloat);
+  private native long ffmpegInitialize(
+      String codecName,
+      @Nullable byte[] extraData,
+      boolean outputFloat,
+      int rawSampleRate,
+      int rawChannelCount);
+
   private native int ffmpegDecode(long context, ByteBuffer inputData, int inputSize,
       ByteBuffer outputData, int outputSize);
   private native int ffmpegGetChannelCount(long context);
   private native int ffmpegGetSampleRate(long context);
-  private native long ffmpegReset(long context, byte[] extraData);
+
+  private native long ffmpegReset(long context, @Nullable byte[] extraData);
+
   private native void ffmpegRelease(long context);
 
 }

extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegLibrary.java

@@ -15,6 +15,8 @@
  */
 package com.google.android.exoplayer2.ext.ffmpeg;
 
+import android.support.annotation.Nullable;
+import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.util.LibraryLoader;
 import com.google.android.exoplayer2.util.MimeTypes;
@@ -51,10 +53,8 @@ public final class FfmpegLibrary {
     return LOADER.isAvailable();
   }
 
-  /**
-   * Returns the version of the underlying library if available, or null otherwise.
-   */
-  public static String getVersion() {
+  /** Returns the version of the underlying library if available, or null otherwise. */
+  public static @Nullable String getVersion() {
     return isAvailable() ? ffmpegGetVersion() : null;
   }
 
@@ -62,19 +62,21 @@ public final class FfmpegLibrary {
    * Returns whether the underlying library supports the specified MIME type.
    *
    * @param mimeType The MIME type to check.
+   * @param encoding The PCM encoding for raw audio.
    */
-  public static boolean supportsFormat(String mimeType) {
+  public static boolean supportsFormat(String mimeType, @C.PcmEncoding int encoding) {
     if (!isAvailable()) {
       return false;
     }
-    String codecName = getCodecName(mimeType);
+    String codecName = getCodecName(mimeType, encoding);
     return codecName != null && ffmpegHasDecoder(codecName);
   }
 
   /**
-   * Returns the name of the FFmpeg decoder that could be used to decode {@code mimeType}.
+   * Returns the name of the FFmpeg decoder that could be used to decode the format, or {@code null}
+   * if it's unsupported.
    */
-  /* package */ static String getCodecName(String mimeType) {
+  /* package */ static @Nullable String getCodecName(String mimeType, @C.PcmEncoding int encoding) {
     switch (mimeType) {
       case MimeTypes.AUDIO_AAC:
         return "aac";
@@ -103,6 +105,14 @@ public final class FfmpegLibrary {
         return "flac";
       case MimeTypes.AUDIO_ALAC:
         return "alac";
+      case MimeTypes.AUDIO_RAW:
+        if (encoding == C.ENCODING_PCM_MU_LAW) {
+          return "pcm_mulaw";
+        } else if (encoding == C.ENCODING_PCM_A_LAW) {
+          return "pcm_alaw";
+        } else {
+          return null;
+        }
       default:
         return null;
     }

extensions/ffmpeg/src/main/jni/ffmpeg_jni.cc

@@ -27,6 +27,7 @@ extern "C" {
 #endif
 #include <libavcodec/avcodec.h>
 #include <libavresample/avresample.h>
+#include <libavutil/channel_layout.h>
 #include <libavutil/error.h>
 #include <libavutil/opt.h>
 }
@@ -72,8 +73,9 @@ AVCodec *getCodecByName(JNIEnv* env, jstring codecName);
  * provided extraData as initialization data for the decoder if it is non-NULL.
  * Returns the created context.
  */
-AVCodecContext *createContext(JNIEnv *env, AVCodec *codec,
-                              jbyteArray extraData, jboolean outputFloat);
+AVCodecContext *createContext(JNIEnv *env, AVCodec *codec, jbyteArray extraData,
+                              jboolean outputFloat, jint rawSampleRate,
+                              jint rawChannelCount);
 
 /**
  * Decodes the packet into the output buffer, returning the number of bytes
@@ -110,13 +112,14 @@ LIBRARY_FUNC(jboolean, ffmpegHasDecoder, jstring codecName) {
 }
 
 DECODER_FUNC(jlong, ffmpegInitialize, jstring codecName, jbyteArray extraData,
-    jboolean outputFloat) {
+             jboolean outputFloat, jint rawSampleRate, jint rawChannelCount) {
   AVCodec *codec = getCodecByName(env, codecName);
   if (!codec) {
     LOGE("Codec not found.");
     return 0L;
   }
-  return (jlong) createContext(env, codec, extraData, outputFloat);
+  return (jlong)createContext(env, codec, extraData, outputFloat, rawSampleRate,
+                              rawChannelCount);
 }
 
 DECODER_FUNC(jint, ffmpegDecode, jlong context, jobject inputData,
@@ -180,8 +183,11 @@ DECODER_FUNC(jlong, ffmpegReset, jlong jContext, jbyteArray extraData) {
       LOGE("Unexpected error finding codec %d.", codecId);
       return 0L;
     }
-    return (jlong) createContext(env, codec, extraData,
-        context->request_sample_fmt == OUTPUT_FORMAT_PCM_FLOAT);
+    jboolean outputFloat =
+        (jboolean)(context->request_sample_fmt == OUTPUT_FORMAT_PCM_FLOAT);
+    return (jlong)createContext(env, codec, extraData, outputFloat,
+                                /* rawSampleRate= */ -1,
+                                /* rawChannelCount= */ -1);
   }
 
   avcodec_flush_buffers(context);
@@ -204,8 +210,9 @@ AVCodec *getCodecByName(JNIEnv* env, jstring codecName) {
   return codec;
 }
 
-AVCodecContext *createContext(JNIEnv *env, AVCodec *codec,
-                              jbyteArray extraData, jboolean outputFloat) {
+AVCodecContext *createContext(JNIEnv *env, AVCodec *codec, jbyteArray extraData,
+                              jboolean outputFloat, jint rawSampleRate,
+                              jint rawChannelCount) {
   AVCodecContext *context = avcodec_alloc_context3(codec);
   if (!context) {
     LOGE("Failed to allocate context.");
@@ -225,6 +232,12 @@ AVCodecContext *createContext(JNIEnv *env, AVCodec *codec,
     }
     env->GetByteArrayRegion(extraData, 0, size, (jbyte *) context->extradata);
   }
+  if (context->codec_id == AV_CODEC_ID_PCM_MULAW ||
+      context->codec_id == AV_CODEC_ID_PCM_ALAW) {
+    context->sample_rate = rawSampleRate;
+    context->channels = rawChannelCount;
+    context->channel_layout = av_get_default_channel_layout(rawChannelCount);
+  }
   int result = avcodec_open2(context, codec, NULL);
   if (result < 0) {
     logError("avcodec_open2", result);

library/core/src/main/java/com/google/android/exoplayer2/C.java

@@ -136,6 +136,8 @@ public final class C {
     ENCODING_PCM_24BIT,
     ENCODING_PCM_32BIT,
     ENCODING_PCM_FLOAT,
+    ENCODING_PCM_MU_LAW,
+    ENCODING_PCM_A_LAW,
     ENCODING_AC3,
     ENCODING_E_AC3,
     ENCODING_DTS,
@@ -144,12 +146,19 @@ public final class C {
   })
   public @interface Encoding {}
 
-  /**
-   * Represents a PCM audio encoding, or an invalid or unset value.
-   */
+  /** Represents a PCM audio encoding, or an invalid or unset value. */
   @Retention(RetentionPolicy.SOURCE)
-  @IntDef({Format.NO_VALUE, ENCODING_INVALID, ENCODING_PCM_8BIT, ENCODING_PCM_16BIT,
-      ENCODING_PCM_24BIT, ENCODING_PCM_32BIT, ENCODING_PCM_FLOAT})
+  @IntDef({
+    Format.NO_VALUE,
+    ENCODING_INVALID,
+    ENCODING_PCM_8BIT,
+    ENCODING_PCM_16BIT,
+    ENCODING_PCM_24BIT,
+    ENCODING_PCM_32BIT,
+    ENCODING_PCM_FLOAT,
+    ENCODING_PCM_MU_LAW,
+    ENCODING_PCM_A_LAW
+  })
   public @interface PcmEncoding {}
   /** @see AudioFormat#ENCODING_INVALID */
   public static final int ENCODING_INVALID = AudioFormat.ENCODING_INVALID;
@@ -163,6 +172,10 @@ public final class C {
   public static final int ENCODING_PCM_32BIT = 0x40000000;
   /** @see AudioFormat#ENCODING_PCM_FLOAT */
   public static final int ENCODING_PCM_FLOAT = AudioFormat.ENCODING_PCM_FLOAT;
+  /** Audio encoding for mu-law. */
+  public static final int ENCODING_PCM_MU_LAW = 0x10000000;
+  /** Audio encoding for A-law. */
+  public static final int ENCODING_PCM_A_LAW = 0x20000000;
   /** @see AudioFormat#ENCODING_AC3 */
   public static final int ENCODING_AC3 = AudioFormat.ENCODING_AC3;
   /** @see AudioFormat#ENCODING_E_AC3 */

library/core/src/main/java/com/google/android/exoplayer2/Format.java

@@ -125,12 +125,12 @@ public final class Format implements Parcelable {
   public final int sampleRate;
   /**
    * The encoding for PCM audio streams. If {@link #sampleMimeType} is {@link MimeTypes#AUDIO_RAW}
-   * then one of {@link C#ENCODING_PCM_8BIT}, {@link C#ENCODING_PCM_16BIT},
-   * {@link C#ENCODING_PCM_24BIT} and {@link C#ENCODING_PCM_32BIT}. Set to {@link #NO_VALUE} for
-   * other media types.
+   * then one of {@link C#ENCODING_PCM_8BIT}, {@link C#ENCODING_PCM_16BIT}, {@link
+   * C#ENCODING_PCM_24BIT}, {@link C#ENCODING_PCM_32BIT}, {@link C#ENCODING_PCM_FLOAT}, {@link
+   * C#ENCODING_PCM_MU_LAW} or {@link C#ENCODING_PCM_A_LAW}. Set to {@link #NO_VALUE} for other
+   * media types.
    */
-  @C.PcmEncoding
-  public final int pcmEncoding;
+  public final @C.PcmEncoding int pcmEncoding;
   /**
    * The number of frames to trim from the start of the decoded audio stream, or 0 if not
    * applicable.

library/core/src/main/java/com/google/android/exoplayer2/audio/AudioTrackPositionTracker.java

@@ -193,7 +193,7 @@ import java.lang.reflect.Method;
     audioTimestampPoller = new AudioTimestampPoller(audioTrack);
     outputSampleRate = audioTrack.getSampleRate();
     needsPassthroughWorkarounds = needsPassthroughWorkarounds(outputEncoding);
-    isOutputPcm = Util.isEncodingPcm(outputEncoding);
+    isOutputPcm = Util.isEncodingLinearPcm(outputEncoding);
     bufferSizeUs = isOutputPcm ? framesToDurationUs(bufferSize / outputPcmFrameSize) : C.TIME_UNSET;
     lastRawPlaybackHeadPosition = 0;
     rawPlaybackHeadWrapCount = 0;

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -371,7 +371,7 @@ public final class DefaultAudioSink implements AudioSink {
 
   @Override
   public boolean isEncodingSupported(@C.Encoding int encoding) {
-    if (Util.isEncodingPcm(encoding)) {
+    if (Util.isEncodingLinearPcm(encoding)) {
       // AudioTrack supports 16-bit integer PCM output in all platform API versions, and float
       // output from platform API version 21 only. Other integer PCM encodings are resampled by this
       // sink to 16-bit PCM.
@@ -405,7 +405,7 @@ public final class DefaultAudioSink implements AudioSink {
     this.inputSampleRate = inputSampleRate;
     int channelCount = inputChannelCount;
     int sampleRate = inputSampleRate;
-    isInputPcm = Util.isEncodingPcm(inputEncoding);
+    isInputPcm = Util.isEncodingLinearPcm(inputEncoding);
     shouldConvertHighResIntPcmToFloat =
         enableConvertHighResIntPcmToFloat
             && isEncodingSupported(C.ENCODING_PCM_32BIT)

library/core/src/main/java/com/google/android/exoplayer2/audio/SimpleDecoderAudioRenderer.java

@@ -20,6 +20,7 @@ import android.os.Handler;
 import android.os.Looper;
 import android.os.SystemClock;
 import android.support.annotation.IntDef;
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.BaseRenderer;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlaybackException;
@@ -121,7 +122,9 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
    * @param eventListener A listener of events. May be null if delivery of events is not required.
    * @param audioProcessors Optional {@link AudioProcessor}s that will process audio before output.
    */
-  public SimpleDecoderAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
+  public SimpleDecoderAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
       AudioProcessor... audioProcessors) {
     this(
         eventHandler,
@@ -139,8 +142,10 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
    * @param audioCapabilities The audio capabilities for playback on this device. May be null if the
    *     default capabilities (no encoded audio passthrough support) should be assumed.
    */
-  public SimpleDecoderAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
-      AudioCapabilities audioCapabilities) {
+  public SimpleDecoderAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
+      @Nullable AudioCapabilities audioCapabilities) {
     this(
         eventHandler,
         eventListener,
@@ -164,9 +169,13 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
    *     has obtained the keys necessary to decrypt encrypted regions of the media.
    * @param audioProcessors Optional {@link AudioProcessor}s that will process audio before output.
    */
-  public SimpleDecoderAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
-      AudioCapabilities audioCapabilities, DrmSessionManager<ExoMediaCrypto> drmSessionManager,
-      boolean playClearSamplesWithoutKeys, AudioProcessor... audioProcessors) {
+  public SimpleDecoderAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
+      @Nullable AudioCapabilities audioCapabilities,
+      @Nullable DrmSessionManager<ExoMediaCrypto> drmSessionManager,
+      boolean playClearSamplesWithoutKeys,
+      AudioProcessor... audioProcessors) {
     this(eventHandler, eventListener, drmSessionManager,
         playClearSamplesWithoutKeys, new DefaultAudioSink(audioCapabilities, audioProcessors));
   }
@@ -184,8 +193,11 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
    *     has obtained the keys necessary to decrypt encrypted regions of the media.
    * @param audioSink The sink to which audio will be output.
    */
-  public SimpleDecoderAudioRenderer(Handler eventHandler, AudioRendererEventListener eventListener,
-      DrmSessionManager<ExoMediaCrypto> drmSessionManager, boolean playClearSamplesWithoutKeys,
+  public SimpleDecoderAudioRenderer(
+      @Nullable Handler eventHandler,
+      @Nullable AudioRendererEventListener eventListener,
+      @Nullable DrmSessionManager<ExoMediaCrypto> drmSessionManager,
+      boolean playClearSamplesWithoutKeys,
       AudioSink audioSink) {
     super(C.TRACK_TYPE_AUDIO);
     this.drmSessionManager = drmSessionManager;

library/core/src/main/java/com/google/android/exoplayer2/decoder/SimpleDecoder.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.decoder;
 
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.Assertions;
 import java.util.ArrayDeque;
@@ -292,14 +293,13 @@ public abstract class SimpleDecoder<I extends DecoderInputBuffer, O extends Outp
    * Decodes the {@code inputBuffer} and stores any decoded output in {@code outputBuffer}.
    *
    * @param inputBuffer The buffer to decode.
-   * @param outputBuffer The output buffer to store decoded data. The flag
-   *     {@link C#BUFFER_FLAG_DECODE_ONLY} will be set if the same flag is set on
-   *     {@code inputBuffer}, but may be set/unset as required. If the flag is set when the call
-   *     returns then the output buffer will not be made available to dequeue. The output buffer
-   *     may not have been populated in this case.
+   * @param outputBuffer The output buffer to store decoded data. The flag {@link
+   *     C#BUFFER_FLAG_DECODE_ONLY} will be set if the same flag is set on {@code inputBuffer}, but
+   *     may be set/unset as required. If the flag is set when the call returns then the output
+   *     buffer will not be made available to dequeue. The output buffer may not have been populated
+   *     in this case.
    * @param reset Whether the decoder must be reset before decoding.
    * @return A decoder exception if an error occurred, or null if decoding was successful.
    */
-  protected abstract E decode(I inputBuffer, O outputBuffer, boolean reset);
-
+  protected abstract @Nullable E decode(I inputBuffer, O outputBuffer, boolean reset);
 }

library/core/src/main/java/com/google/android/exoplayer2/extractor/wav/WavHeaderReader.java

@@ -33,6 +33,10 @@ import java.io.IOException;
   private static final int TYPE_PCM = 0x0001;
   /** Float PCM audio data. */
   private static final int TYPE_FLOAT = 0x0003;
+  /** 8-bit ITU-T G.711 A-law audio data. */
+  private static final int TYPE_A_LAW = 0x0006;
+  /** 8-bit ITU-T G.711 mu-law audio data. */
+  private static final int TYPE_MU_LAW = 0x0007;
   /** Extended WAVE format. */
   private static final int TYPE_WAVE_FORMAT_EXTENSIBLE = 0xFFFE;
 
@@ -98,6 +102,12 @@ import java.io.IOException;
       case TYPE_FLOAT:
         encoding = bitsPerSample == 32 ? C.ENCODING_PCM_FLOAT : C.ENCODING_INVALID;
         break;
+      case TYPE_A_LAW:
+        encoding = C.ENCODING_PCM_A_LAW;
+        break;
+      case TYPE_MU_LAW:
+        encoding = C.ENCODING_PCM_MU_LAW;
+        break;
       default:
         Log.e(TAG, "Unsupported WAV format type: " + type);
         return null;

library/core/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -1092,12 +1092,12 @@ public final class Util {
   }
 
   /**
-   * Returns whether {@code encoding} is one of the PCM encodings.
+   * Returns whether {@code encoding} is one of the linear PCM encodings.
    *
    * @param encoding The encoding of the audio data.
    * @return Whether the encoding is one of the PCM encodings.
    */
-  public static boolean isEncodingPcm(@C.Encoding int encoding) {
+  public static boolean isEncodingLinearPcm(@C.Encoding int encoding) {
     return encoding == C.ENCODING_PCM_8BIT
         || encoding == C.ENCODING_PCM_16BIT
         || encoding == C.ENCODING_PCM_24BIT