content: /*
   * Copyright (C) 2017 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.audio;
  
  import androidx.annotation.Nullable;
  import com.google.android.exoplayer2.C;
  import com.google.android.exoplayer2.Format;
  import com.google.android.exoplayer2.util.Assertions;
  import com.google.errorprone.annotations.CanIgnoreReturnValue;
  import java.nio.ByteBuffer;
  
  /**
   * An {@link AudioProcessor} that applies a mapping from input channels onto specified output
   * channels. This can be used to reorder, duplicate or discard channels.
   */
  /* package */ final class ChannelMappingAudioProcessor extends BaseAudioProcessor {
  
    @Nullable private int[] pendingOutputChannels;
    @Nullable private int[] outputChannels;
  
    /**
     * Resets the channel mapping. After calling this method, call {@link #configure(AudioFormat)} to
     * start using the new channel map.
     *
     * <p>See {@link AudioSink#configure(Format, int, int[])}.
     *
     * @param outputChannels The mapping from input to output channel indices, or {@code null} to
     *     leave the input unchanged.
     */
    public void setChannelMap(@Nullable int[] outputChannels) {
      pendingOutputChannels = outputChannels;
    }
  
    @Override
    @CanIgnoreReturnValue
    public AudioFormat onConfigure(AudioFormat inputAudioFormat)
        throws UnhandledAudioFormatException {
      @Nullable int[] outputChannels = pendingOutputChannels;
      if (outputChannels == null) {
        return AudioFormat.NOT_SET;
      }
  
      if (inputAudioFormat.encoding != C.ENCODING_PCM_16BIT) {
        throw new UnhandledAudioFormatException(inputAudioFormat);
      }
  
      boolean active = inputAudioFormat.channelCount != outputChannels.length;
      for (int i = 0; i < outputChannels.length; i++) {
        int channelIndex = outputChannels[i];
        if (channelIndex >= inputAudioFormat.channelCount) {
          throw new UnhandledAudioFormatException(inputAudioFormat);
        }
        active |= (channelIndex != i);
      }
      return active
          ? new AudioFormat(inputAudioFormat.sampleRate, outputChannels.length, C.ENCODING_PCM_16BIT)
          : AudioFormat.NOT_SET;
    }
  
    @Override
    public void queueInput(ByteBuffer inputBuffer) {
      int[] outputChannels = Assertions.checkNotNull(this.outputChannels);
      int position = inputBuffer.position();
      int limit = inputBuffer.limit();
      int frameCount = (limit - position) / inputAudioFormat.bytesPerFrame;
      int outputSize = frameCount * outputAudioFormat.bytesPerFrame;
      ByteBuffer buffer = replaceOutputBuffer(outputSize);
      while (position < limit) {
        for (int channelIndex : outputChannels) {
          buffer.putShort(inputBuffer.getShort(position + 2 * channelIndex));
        }
        position += inputAudioFormat.bytesPerFrame;
      }
      inputBuffer.position(limit);
      buffer.flip();
    }
  
    @Override
    protected void onFlush() {
      outputChannels = pendingOutputChannels;
    }
  
    @Override
    protected void onReset() {
      outputChannels = null;
      pendingOutputChannels = null;
    }
  }
  