媒体提取器显示“未能实例化提取器”

Question

我试图在android上开发用于OGG文件格式音频流的媒体提取器。我在google文档的帮助下编写了一些代码。但根本不起作用。可能我写错了代码或语法，因为我是学生。它显示我无法实例化提取器

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

MediaExtractor extractor = new MediaExtractor();
extractor.setDataSource("http://examplelink.com/ogg");// I cant put real link so sorry for that
int numTracks = extractor.getTrackCount();
for (int i = 0; i < numTracks; ++i) {
    MediaFormat format = extractor.getTrackFormat(i);
    String mime = format.getString(MediaFormat.KEY_MIME);
    extractor.selectTrack(i);

    ByteBuffer inputBuffer = ByteBuffer.allocate(1024);
    while (extractor.readSampleData(inputBuffer,0) >= 0) {
            int trackIndex = (int) extractor.getSampleTime();
            long presentationTimeUs = extractor.getSampleTime();
    }

    MediaCodec codec = MediaCodec.createDecoderByType(mime);
    codec.configure(format, null /* surface */, null /* crypto */, 0 /* flags */);
    codec.start();
    ByteBuffer[] inputBuffers = codec.getInputBuffers();
    ByteBuffer[] outputBuffers = codec.getOutputBuffers();
    format = codec.getOutputFormat();
    Long timeoutUs=(long) 1;
    for (;;) {
        int inputBufferIndex = codec.dequeueInputBuffer(timeoutUs);
        if (inputBufferIndex >= 0) {
            // fill inputBuffers[inputBufferIndex] with valid data
            codec.queueInputBuffer(inputBufferIndex, 0, 128, 0,0);
        }
        MediaCodec.BufferInfo info = new BufferInfo();
        int outputBufferIndex = codec.dequeueOutputBuffer(info, timeoutUs);
        if (outputBufferIndex >= 0) {
            // outputBuffer is ready to be processed or rendered.
            codec.releaseOutputBuffer(outputBufferIndex, false);
        } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
            outputBuffers = codec.getOutputBuffers();
        } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
            // Subsequent data will conform to new format.
            format = codec.getOutputFormat();
            AudioTrack mAudioTrack = null;
            mAudioTrack.setPlaybackRate(format.getInteger(MediaFormat.KEY_SAMPLE_RATE));
        }
        codec.stop();
        codec.release();
        codec = null;
    }
}

}

Answer 1

我想你的问题是“为什么它根本不起作用？”通常，这是一个太大的问题，但在这种情况下，我认为您根本不了解MediaExtractor & MediaCodec是如何工作的。

但并不全是你的错。说得好听些，这份文件很神秘。但是，我成功地用这种方式播放了音频文件。

我的方案假设MediaCodec实现一个异步缓冲区队列。这个队列中似乎有大约4个缓冲区。

因此，我使用两个线程:一个线程将来自MediaExtractor的数据放入队列，另一个线程从队列中取出解码音频并将其写入AudioTrack。

然后，我需要非常小心，以避免死锁在一个寻求，例如。最后我得到的代码比你的多得多。我不知道该怎么避免！

我在考虑试一试视频。任何有帮助的参考资料将不胜感激！

完成

Answer 2

下面的代码将为我在JB平台上的本地音频文件完美地工作。

try{
  Extractor lExt = new MediaExtractor();
  lExt.setDataSource(file path); //I have tried with local file
  lExt.setTrack(0); //For local file only one track will be present
  MediaFormat format = lExt.getTrackFormat(0); //0 is the track ID
  String mime = format.getString(MediaFormat.KEY_MIME);
  MediaCodec codec = MediaCodec.createDecoderByType(mime);
  codec.configure(
       format,//format of input data ::decoder OR desired format of the output data:encoder
       null,//Specify a surface on which to render the output of this decoder
       null,//Specify a crypto object to facilitate secure decryption
       0 //For Decoding, encoding use: CONFIGURE_FLAG_ENCODE 
       );
  codec.start();
  codec.flush();

  //Get Input and Output buffers from codec
  inputBuffers = codec.getInputBuffers();
  outputBuffers = codec.getOutputBuffers(); 

  While(condition)
  {
      //Get Audio data from extractor
      int inputBufIndex = codec.dequeueInputBuffer(50);//Timeout set of 50 microsec
      if (inputBufIndex >= 0) 
      {
           ByteBuffer dstBuf = inputBuffers[inputBufIndex]; 
           int sampleSize = extractor.readSampleData(dstBuf, 0);
           long presentationTimeUs = extractor.getSampleTime();

           codec.queueInputBuffer(inputBufIndex,
                           0, //offset
                           sampleSize,
                           presentationTimeUs,
                           0); //Use appropriate flag value
           extractor.advance();
        }

      //Use codec to decode the data -- handle end of stream properly
        MediaCodec.BufferInfo info = new  MediaCodec.BufferInfo();
        info.set(0,0,0,0);
        final int res = codec.dequeueOutputBuffer(info, 20000);
        if (res >= 0) 
        {
            int outputBufIndex = res;
            ByteBuffer buf = outputBuffers[outputBufIndex];

            byte[] chunk = new byte[info.size];
            buf.get(chunk); // Read the buffer all at once
            buf.clear(); // ** MUST DO!!! OTHERWISE THE NEXT TIME YOU GET THIS SAME BUFFER BAD THINGS WILL HAPPEN

            if (chunk.length > 0) 
               //Use this chunk as it contains decoded audio dat            
            codec.releaseOutputBuffer(outputBufIndex, false /* render */); 
        } 
        else if (res == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) 
            outputBuffers = codec.getOutputBuffers();
  }
  codec.stop();
  codec.release();
  lExt.release();
}
catch(Exception ex)...

Answer 3

将数据源设置为远程URL将需要在android.permission.INTERNET中声明AndroidManifest.xml权限

<uses-permission android:name="android.permission.INTERNET" />