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Android MediaCodec硬编解码器

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Android 的 MediaCodec 可以编/解码音频视频，支持同步和异步两种使用方式。

异步

参考官网的文档

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MediaCodec codec = MediaCodec.createByCodecName(name);
 MediaFormat mOutputFormat; // member variable
 codec.setCallback(new MediaCodec.Callback() {
  @Override
  void onInputBufferAvailable(MediaCodec mc, int inputBufferId) {
    ByteBuffer inputBuffer = codec.getInputBuffer(inputBufferId);
    // fill inputBuffer with valid data
    …
    codec.queueInputBuffer(inputBufferId, …);
  }
 
  @Override
  void onOutputBufferAvailable(MediaCodec mc, int outputBufferId, …) {
    ByteBuffer outputBuffer = codec.getOutputBuffer(outputBufferId);
    MediaFormat bufferFormat = codec.getOutputFormat(outputBufferId); // option A
    // bufferFormat is equivalent to mOutputFormat
    // outputBuffer is ready to be processed or rendered.
    …
    codec.releaseOutputBuffer(outputBufferId, …);
  }
 
  @Override
  void onOutputFormatChanged(MediaCodec mc, MediaFormat format) {
    // Subsequent data will conform to new format.
    // Can ignore if using getOutputFormat(outputBufferId)
    mOutputFormat = format; // option B
  }
 
  @Override
  void onError(…) {
    …
  }
 });
 codec.configure(format, …);
 mOutputFormat = codec.getOutputFormat(); // option B
 codec.start();
 // wait for processing to complete
 codec.stop();
 codec.release();

音频和视频的用法差不多，差异在于配置上，编码和解码也是。

两个不同的函数 MediaCodec.createDecoderByType(..) 为 MediaCodec.createEncoderByType(..) 创建 MediaCodec 。

  1. 实现一个异步音频的编码器
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/**
 * @param mime MediaFormat.MIMETYPE_AUDIO_*
 */
fun createMediaCodecEncoder(mime: String, sampleRate:Int){

    val format = MediaFormat.createAudioFormat(mime,sampleRate,1)
    format.setInteger(MediaFormat.KEY_CHANNEL_MASK, AudioFormat.CHANNEL_IN_MONO);
    format.setInteger(MediaFormat.KEY_BIT_RATE, 128000)

    val mMediaCodec = MediaCodec.createEncoderByType(mime)
    mMediaCodec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE)

    mMediaCodec.setCallback(object :MediaCodec.Callback(){

        /**
         * 输入缓冲区可用时回调此函数
         */
        override fun onInputBufferAvailable(codec: MediaCodec, index: Int) {
            //TODO 这里输入数据
            val dataLength = 2
            val data = ByteArray(dataLength)//TODO 假设这是一帧PCM数据，作为输入编码器的数据
            val inputBuffer = codec.getInputBuffer(index)
            if(inputBuffer != null){
                inputBuffer.clear()
                inputBuffer.put(data)
                codec.queueInputBuffer(index,0,dataLength,0,0)
            }else{
                codec.queueInputBuffer(index,0,0,0,0)
            }
        }

        /**
         * 输出编码数据
         */
        override fun onOutputBufferAvailable(
            codec: MediaCodec,
            index: Int,
            info: MediaCodec.BufferInfo ) {
            try {
                if(info.size > 0){

                    if ((info.flags and MediaCodec.BUFFER_FLAG_CODEC_CONFIG) != 0) {
                        println("编码器输出配置信息")
                    }else{
                        println("编码器输出编码数据")
                    }

                    val outputBuffer = codec.getOutputBuffer(index)//取出数据
                    val outputData = ByteArray(info.size)
                    outputBuffer?.get(outputData)
                    //TODO outputData 是编码后数据
                }
            }catch (e:Exception){
                e.printStackTrace()
            }finally {
                codec.releaseOutputBuffer(index, false)
            }
        }

        override fun onError(codec: MediaCodec, e: MediaCodec.CodecException) {
            e.printStackTrace()
        }

        override fun onOutputFormatChanged(codec: MediaCodec, format: MediaFormat) {
            println("onOutputFormatChanged")
        }
    })
    mMediaCodec.start()
}

  1. 实现一个异步音频的解码器
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/**
 * @param mime MediaFormat.MIMETYPE_AUDIO_*
 */
fun createMediaCodecDecoder(mime: String, sampleRate:Int){

    val format = MediaFormat.createAudioFormat(mime,sampleRate,1)
    format.setInteger(MediaFormat.KEY_CHANNEL_MASK, AudioFormat.CHANNEL_IN_MONO);
    format.setInteger(MediaFormat.KEY_BIT_RATE, 128000)

    val mMediaCodec = MediaCodec.createDecoderByType(mime)
    mMediaCodec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE)

    mMediaCodec.setCallback(object :MediaCodec.Callback(){

        /**
         * 输入缓冲区可用时回调此函数
         */
        override fun onInputBufferAvailable(codec: MediaCodec, index: Int) {

        	//TODO 这里输入数据
            val dataLength = 2
            val data = ByteArray(dataLength)//TODO 假设这是一帧ACC格式数据，作为输入解码器的数据
            val inputBuffer = codec.getInputBuffer(index)
            if(inputBuffer != null){
                inputBuffer.clear()
                inputBuffer.put(data)
                codec.queueInputBuffer(index,0,dataLength,0,0)
            }else{
                codec.queueInputBuffer(index,0,0,0,0)
            }
        }

        /**
         * 输出编码数据
         */
        override fun onOutputBufferAvailable(
            codec: MediaCodec,
            index: Int,
            info: MediaCodec.BufferInfo ) {
            try {
                if(info.size > 0){

                    if ((info.flags and MediaCodec.BUFFER_FLAG_CODEC_CONFIG) != 0) {
                        println("解码器输出配置信息")
                    }else{
                        println("解码器输出编码数据")
                    }

                    val outputBuffer = codec.getOutputBuffer(index)//取出数据
                    val outputData = ByteArray(info.size)
                    outputBuffer?.get(outputData)
                    //TODO outputData 是解码后PCM数据，可以用AudioTrack播放
                }
            }catch (e:Exception){
                e.printStackTrace()
            }finally {
                codec.releaseOutputBuffer(index, false)
            }
        }

        override fun onError(codec: MediaCodec, e: MediaCodec.CodecException) {
            e.printStackTrace()
        }

        override fun onOutputFormatChanged(codec: MediaCodec, format: MediaFormat) {
            println("onOutputFormatChanged")
        }
    })
    mMediaCodec.start()
}

同步

参考官网

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MediaCodec codec = MediaCodec.createByCodecName(name);
 codec.configure(format, …);
 MediaFormat outputFormat = codec.getOutputFormat(); // option B
 codec.start();
 for (;;) {
  int inputBufferId = codec.dequeueInputBuffer(timeoutUs);
  if (inputBufferId >= 0) {
    ByteBuffer inputBuffer = codec.getInputBuffer(…);
    // fill inputBuffer with valid data
    …
    codec.queueInputBuffer(inputBufferId, …);
  }
  int outputBufferId = codec.dequeueOutputBuffer(…);
  if (outputBufferId >= 0) {
    ByteBuffer outputBuffer = codec.getOutputBuffer(outputBufferId);
    MediaFormat bufferFormat = codec.getOutputFormat(outputBufferId); // option A
    // bufferFormat is identical to outputFormat
    // outputBuffer is ready to be processed or rendered.
    …
    codec.releaseOutputBuffer(outputBufferId, …);
  } else if (outputBufferId == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
    // Subsequent data will conform to new format.
    // Can ignore if using getOutputFormat(outputBufferId)
    outputFormat = codec.getOutputFormat(); // option B
  }
 }
 codec.stop();
 codec.release();

实现一个同步音频解码器（伪代码）

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MediaCodec codec = MediaCodec.createDecoderByType(MediaFormat.MIMETYPE_AUDIO_G711_ALAW);
final MediaFormat format = MediaFormat.createAudioFormat(
        MediaFormat.MIMETYPE_AUDIO_G711_ALAW,
        8000,
        1);
format.setInteger(MediaFormat.KEY_BIT_RATE, 128000);
codec.configure(format,null,null,0);
codec.start();
inputBuffers = codec.getInputBuffers();

while (true){
    int inputIndex = codec.dequeueInputBuffer(0);
    if(inputIndex > -1){
        ByteBuffer inputBuffer = inputBuffers[inputIndex];
        inputBuffer.clear();

        //假如这是输入需要解码的G711A格式数据，
        int aacLength = 2;
        byte[] g711Buffer = new byte[aacLength];

        inputBuffer.put(g711Buffer, 0, aacLength);
        codec.queueInputBuffer(inputIndex, 0, aacLength, 0, 0);
        MediaCodec.BufferInfo infoOutput = new MediaCodec.BufferInfo();
        int outputIndex = codec.dequeueOutputBuffer(infoOutput,10);
        if (outputIndex >= 0) {
            ByteBuffer outputBuffer = codec.getOutputBuffer(outputIndex);
            byte[] outputData = new byte[infoOutput.size];
            outputBuffer.get(outputData);

            //TODO 这是输出的PCM数据

            codec.releaseOutputBuffer(outputIndex, false);
        }
    }
}

同步编码器类似，省略。